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Are HRVs Cost-Effective?

Compared to a simple exhaust fan, a heat-recovery ventilator saves energy — but it probably won’t save enough to justify the high cost of the equipment

Posted on Dec 7 2012 by Martin Holladay

From 1977 (when the Saskatchewan Conservation house was built) until 2004 (when the first U.S. Passivhaus was built), North American builders completed hundreds of superinsulated homes. In those days, anyone interested in rating the performance of these homes was probably interested in just one metric: annual energy use.

Over the last eight years, however, with the increasing attention paid to the Passivhaus standard, some builders of superinsulated homes are walking along a narrower path. Any builder interested in achieving the Passivhaus standard soon learns that a low energy bill is no longer sufficient to gain accolades.

Unexamined postulates

This narrow Passivhaus path has several restrictions; I call them “unexamined Passivhaus postulates.” Like postulates in geometry, Passivhaus postulates need not be proven; they just are. Here are four of the postulates:

  • It makes sense to deliver space heat through ventilation ductwork.
  • It’s more important to achieve 15 kWh/m2•year and 0.6 ach50 that to calculate whether these goals are cost-effective.
  • The output of PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. system should not be considered in one’s annual energy calculations.
  • Every house needs an HRV.

These Passivhaus postulates are not equally binding; for example, North American designers have chosen to ignore the postulate that affirms that space heat should be delivered through ventilation ductwork. (Although the principle is widely ignored, it is still prominently featured on ) When I interviewed Dr. Feist in December 2007, he used the same definition for a Passivhaus that is enshrined on Passipedia: “As long as you build a house in a way that you can use the heat-recovery ventilation(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. system — a system that you need anyway for indoor air requirements — to provide the heat and cooling, it can be considered a Passivhaus.”

Each of the four postulates listed above deserves to be examined more closely than it has up until now, because each of these postulates forces Passivhaus designers to follow a narrower path than the one followed by the North American designers of superinsulated homes who worked from 1977 to 2004.

In this article, I’ll address one of the unexamined Passivhaus postulates: the one holding that every house needs an HRV.

Does the Passivhaus standard require an HRV?

The question as to whether the Passivhaus standard requires an HRV is complicated. As far as I know, every Passivhaus in the U.S. includes an HRV or an ERV.

The requirement for an HRV is explained in a rule book published by the Passivhaus Institut in Darmstadt, The book lists “Documents necessary for Passive House certification,” a list which includes: “HRV commissioningProcess of testing a home after a construction or renovation project to ensure that all of the home's systems are operating correctly and at maximum efficiency. report. The results must at least include the following: … name and address of the tester, time of adjustment, ventilation system manufacturer and type of device, adjusted volume flow rates per valve for normal operation, mass flow/volumetric flow balance for outdoor air and exhaust air (maximum disbalance of 10%).”

According to this document, it seems clear that an HRV is required, not optional.

As it turns out, however, the Passivhaus standard doesn't require the use of an HRV. According to Floris Keverling Buisman, a certified Passive House consultant in New York City, “PHI [The Passivhaus Institut] does not require an HRV. ... Why it is generally recommended is that it will be very hard to get your heating (or cooling) demand below 15kWh/m2•year without an HRV in most climates. The tricky part is that if you would like to get certified (voluntarily) you need to conform to all the Passivhaus criteria, which includes comfort — which is defined by ISO 7730 ... If your supply air is more than 3.5°C (6.3°F) lower than the room temperature, your building in my understanding would no longer be comfortable and certifiable by PHI as a Certified Passive House. This is why you need an HRV with a high recovery rate in most climates.”

For most Passivhaus builders, the net result of these requirements is that it is very difficult or impossible to install an exhaust-only or supply-only ventilation system. In essence, the Passivhaus standard pushes builders in the direction of an HRV.

Other ventilation approaches are cheaper

While HRVs do an excellent job of ventilating a house, there are less expensive approaches: either an exhaust-only ventilationMechanical ventilation system in which one or more fans are used to exhaust air from a house and make-up air is supplied passively. Exhaust-only ventilation creates slight depressurization of the home; its impact on vented gas appliances should be considered. system or a supply-only ventilation system. Thousands of superinsulated homes successfully use one of these two approaches.

The main advantage of an HRV is that it recovers some of the heat that would otherwise leave the building with the exhaust air. However, an HRV is an expensive gadget, which raises the question: does this gadget recover enough energy to justify its high cost?

The answer depends on your climate. In a very cold climate, an HRV can recover enough heat to justify its high cost. In moderate climates, however, an HRV doesn’t make much sense.

This analysis raises an interesting question: why have Passivhaus proponents embraced one expensive gadget — the HRV — but rejected another expensive gadget — the PV module? Hint: the answer has nothing to do with cost-effectiveness. In most U.S. climates, an investment in PV modules provides a greater energy return than an equivalent investment in an HRV (or, for that matter, an investment in thick subslab foam).

Modeling HRV energy savings

John Semmelhack, an energy consultant and certified Passivhaus consultant in Charlottesville, Virginia, recently took a fresh look at the question of HRV cost-effectiveness. He reported his findings in a paper, “An energy and economic modeling study of exhaust ventilation systems compared to balanced ventilation systems with energy recovery,” which he presented on September 28, 2012 at the Seventh Annual North American Passive House conference in Denver.

Semmelhack is well aware of the disadvantages of HRVs: “These systems are relatively costly to install compared to other ventilation options, are somewhat complex for owners to operate and maintain, and require a significant amount of fan energy for operation (200-400 kWh/year, about 4-8% of total site energy for a modest-sized, all-electric Passive House). By contrast, well-designed exhaust ventilation systems are less expensive to install, are easier to maintain, and require significantly less fan energy for operation.”

Since he has consulted on several Passivhaus projects, Semmelhack knows exactly how much it costs to install an HRV. He wrote, “In North American Passive Houses, ventilation and space conditioning are often decoupled, requiring separate distribution systems and typically higher upfront cost. It is common for a stand-alone Passive House ventilation system to have an installed cost of $4,000 to $7,000 or more.”

Of course, HRVs recover heat that would otherwise be lost. Semmelhack’s energy modeling exercise showed that “both the ERV and HRV … save energy compared to an exhaust ventilation system in every case in the study.” Although this fact is well known, very few architects and builders have actually calculated how much energy is saved by an HRV compared to a simple exhaust-only ventilation system.

The answer, as it turns out, is not much — unless you live in a very cold climate. In mild climates, a PV array is a better investment than an HRV. Semmelhack wrote, “The amount of site energy saved by the ERV/HRV systems is much lower in the milder climates (330-600 kWh/year) than the colder climates (800-1,100 kWh/year). The lower energy savings in the milder climates leads to poor cost-effectiveness when compared to other energy-saving or energy-producing options such as extra insulation or a photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. system.”

Details of Semmelhack’s modeling exercise

Semmelhack used the Passive House Planning Package (PHPP) to model a single-family three-bedroom house measuring 1,800 square feet. He assumed that the house was heated with an air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps. (for example, a ductless minisplit system), and he assumed that the house achieved a Passivhaus level of airtightness (0.6 ach50).

He modeled the house in six different climates (San Francisco; Atlanta; Charlottesville, Va.; Portland, Or.; Chicago; and Burlington, Vt.) The mildest climate he looked at (San Francisco) has 3,200 heating degree days, while the coldest climate (Burlington, Vt.) has 7,300 heating degree days.

In each climate zone, he modeled the performance of the house with three different ventilation systems: an Ultimate Air 200DX ERV, a Zehnder Comfo 350 HRV, and a Panasonic FV-08VKS3 exhaust fan with variable airflow settings and passive air inlets. The electricity use of each appliance was assumed to be as follows: 0.58 W/cfm for the Ultimate Air ERV, 0.30 W/cfm for the Zehnder HRV, 0.12 W/cfm for the Panasonic exhaust fan. When installed in Chicago and Burlington, the HRV and ERV were assumed to have electric defrost systems.

The ventilation rate was assumed to be 56 cfm continuous for the HRV and ERV, and 64 cfm for the exhaust-only ventilation system “to account for occupant on-demand use of other exhaust appliances: other bath fans (50 cfm x 2 hours/day), range hood (100 cfm x 1 hour/day) and clothes dryer (125 cfm x 1 hour/day).”

By using PHPP software, Semmelhack was able to model aspects of HRV performance that aren’t captured by some other energy-modeling programs. He wrote, “The energy analysis included annual heating demand and latent cooling demand for ventilation and infiltration, ventilation fan energy use, defrost energy use, and space conditioning energy use for ventilation and infiltration.”

What do I get for my investment in an HRV?

To determine whether an HRV is cost-effective in a given climate, Semmelhack had to determine two numbers: the amount of energy saved, and the incremental cost of the equipment compared to an exhaust-only ventilation system.

Semmelhack assumed that the capital costs to install the three studied ventilation systems were as follows:

  • The system with an Ultimate Air ERV cost $4,125 (including ERV, ductwork, fittings, registers, labor, and markup);
  • The system with a Zehnder HRV cost $5,375 (including HRV, ductwork, fittings, registers, labor, and markup);
  • The system with Panasonic fans cost $2,102 (including 3 bath fans, 1 kitchen range hood, ductwork, fittings, labor, and markup).

Some readers will probably note that an exhaust-only ventilation system could be installed for less than Semmelhack assumed; if so, this fact would only strengthen Semmelhack’s conclusions.

Using these figures, Semmelhack calculated that the Ultimate Air ERV represented a $2,023 upcharge from an exhaust-only system, while a Zehnder HRV represented a $3,273 upcharge. He assumed that the lifetime of the ventilation equipment was 20 years.

Using PHPP, Semmelhack calculated the total amount of energy saved over 20 years for the ERV option and the HRV option, compared to the baseline system (the Panasonic exhaust-only system). The energy savings had a cost, of course: the cost of the saved energy over 20 years was equal to the upcharge for the expensive equipment.

Semmelhack concluded, “The cost/kWh saved for the [Ultimate Air] 200DX ranged from as low as $0.12/kWh in Burlington to as high as $0.31/kWh in San Francisco. The cost/kWh saved for the [Zehnder] Comfo 350 ranged from as low as $0.17/kWh in Burlington to as high as $0.41/kWh in Atlanta.”

For purposes of comparison, Semmelhack calculated that the energy generated by a photovoltaic system in Charlottesville, Virginia, costs the owner $0.13/kWh, while the energy saved by an attic insulation upgrade in Charlottesville costs the owner $0.17/kWh. (The results of Semmelhack's energy modeling are shown in greater detail in a bar graph and table, reproduced as Image #2 and Image #3, below).

Semmelhack concluded, “Based on this analysis, the ERV and HRV systems are not cost-effective (compared to the reference points) in terms of energy savings in the milder climates, and are only moderately cost-effective as the house ‘migrates’ to a cold climate (Burlington).”

Passivhaus blinders lead to irrational results

In his paper, Semmelhack takes the bull by the horns and questions why the Passivhaus standard requires the use of an HRV. He wrote, “Based on the poor cost-effectiveness of ERV/HRV systems in the milder climates, it seems irrational that these mechanical systems should be a ‘de facto’ requirement for meeting the annual heat demand requirement for [Passivhaus] certification.”

In , Semmelhack was blunt. “Typical Passive House HRV/ERV systems do not appear to be particularly cost-effective in the milder climates,” he wrote. “We should remove our Passive House blinders and take a closer look at other ventilation options. … PHIUS certification metrics should not have a de-facto mandate for cost-ineffective mechanical systems.”

As PV systems continue to drop in price, the Passivhaus preference for HRVs rather than PV systems gets harder and harder to justify.

HRVs have several benefits

Defenders of HRVs will probably bristle at Semmelhack’s analysis, pointing out that an HRV provides better comfort and delivers fresh air more evenly than does an exhaust-only system. This is undeniable, and some homeowners may be happy to pay thousands of dollars for these benefits.

Others, however, are likely to find that a simple exhaust-only ventilation system meets all of their ventilation needs.

Unexamined postulates come at a cost

The energy-efficiency pioneers who built superinsulated homes from 1977 to 2004 were fairly nimble. They experimented with a variety of approaches to superinsulation, searching for innovative specifications that worked to lower energy consumption.

Compared to these nimble pioneers, Passivhaus designers are dragging around a ball and chain. (Note to Passivhaus designers: If you bend down and look closely at the device fastened to your ankle, you’ll see a small inscription: “Made in Germany.”) The requirement to include an HRV — which many designers interpret as a requirement for an expensive HRV from Europe — is making Passivhaus designers less nimble than other builders.

Years ago, Amory Lovins predicted that superinsulation techniques would allow builders to The concept was later championed by Wolfgang Feist, who predicted that Passivhaus buildings would require less expensive HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. equipment than ordinary buildings.

As it turns out, most Passivhaus builders in the U.S. haven’t been able to tunnel through the HVAC cost barrier — in part because of the burden of unexamined Passivhaus postulates.

There is at least one builder in the U.S. who seems to have managed to tunnel through the HVAC cost barrier, however. I’m thinking of Massachusetts builder Carter Scott. Scott usually specifies simple exhaust-only ventilation systems.

Martin Holladay’s previous blog: “All About Wall Rot.”

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Image Credits:

  1. Photo: Martin Holladay — Bar graph and table: John Semmelhack

Dec 7, 2012 11:33 AM ET

Exhaust Only
by Doug McEvers

HRV/ERV is a balanced system with both supply and exhaust hoods. Exhaust only as I understand it, short of fresh air ports, pulls air through the building envelope leaks to balance the pressure. This air is not filtered and could also cause moisture accumulation in building assemblies.

When one is spending several hundred k on a new home, an extra couple thousand or so for a controlled system may be money well spent.

Dec 7, 2012 12:14 PM ET

Edited Dec 7, 2012 12:16 PM ET.

Response to Doug McEvers
by Martin Holladay

You disparage exhaust-only systems because they pull air through building envelope leaks "short of fresh air ports." But if you read my description of John Semmelhack's modeling exercise, you'll note that he assumed that any exhaust-only ventilation system includes passive air vents.

You are incorrect when you assert that exhaust-only ventilation systems "could cause moisture accumulation in building assemblies." As Bruce Harley has written, “The upper portions (walls and ceilings) of every home — typically most of the second floor in two-story homes — already operate under positive air pressure in cold weather, due to the stack effect. The relatively small airflow of most supply-only ventilation systems (75 cfm to 150 cfm) will have little effect on this situation other than to shift the neutral pressure plane down slightly, in all but the very tightest of homes."

Semmelhack assumed that the air flow of the exhaust-only ventilation system under consideration was only 64 cfm -- even less than the systems Harley was discussing.

Dec 7, 2012 12:56 PM ET

Response to Doug McEvers
by John Semmelhack

I don't disagree with your last sentence - for high-performance homes in the "several hundred thousand dollar" range, a fancier ventilation system may be appropriate for reasons other than energy savings (better control, better filtration, etc.). For more affordable housing, the $2,000-3,000+ savings for a simpler ventilation system can be a big deal.

Yes, exhaust ventilation systems will pull air through building assemblies in all houses. In cold climates, this is usually considered OK, since the outside air generally contains less moisture than the indoor air. In very tight houses that use passive air inlets, the majority of the incoming air will come through the inlets under most conditions.

I'm certainly not advocating exhaust ventilation systems for all climates and all houses. But I do think they make a lot of sense in many situations.

Dec 7, 2012 1:07 PM ET

Passive House certification clarification
by John Semmelhack

Regarding Passive House certification (at least through PHIUS) - there's certainly no requirement for using an ERV/HRV. However, even in mild climates, using an exhaust ventilation system, for example, would require large increases in assembly insulation (over and above typical PH insulation levels!) in order to make up for increased ventilation heat losses and meet the annual heating demand portion of the standard.

Dec 7, 2012 1:17 PM ET

It's worth noting that Katrin
by John Semmelhack

It's worth noting that Katrin Klingenberg at the Passive House Institute U.S. (PHIUS) encouraged me to dig into the details on this topic, after I discussed with her some initial findings. I expect the results will influence (to some degree) the discussions over whether/how to modify the Passive House standard for North American climate zones.

[Editor's note: See Katrin Klingenberg's posted comment on this page -- Comment #50, below.]

Dec 7, 2012 1:37 PM ET

HRV much better IAQ, comfort. Passive inlets ?
by Brian Hludzinski

Great info from John. I'm glad Martin finally mentioned the HRV benefits as I don't see a comparison between an HRV vs exhaust only when talking comfort and IAQ. An Hrv/ERV install (at least ours) have fresh air into all living spaces and exhaust from baths, kitchen , laundry, usually 6 on each side and more for a conditioned crawlspace (2500 SF home). That's a robust system providing great IAQ. I can't see a few continuous bath fans with a few passive inlets comparing to that kind of system. Some rooms without pressuring (bedrooms) will not see as much air exchange. In these homes the HVAC is not coming on very much to move air if that is the strategy. Additionally, as a lot of these homes are going towards point source these even less air movement. None the less, great information.

As far as passive inlets, I'm curious where you would install ? In my cold climate on a winter day, there will be comfort issues.

Dec 7, 2012 1:50 PM ET

Exhaust only problems with bedroom ventilation and combustion
by Kristopher Steege-Reimann

While I strongly agree that strict rules in building often lead to irrational results, I also think that too often computer simulations ignore (or the people interpreting the simulations) ignore the practical variables of real life.

For example, my wife and I have a well insulated and air sealed 550sqft home that didn't have ventilation. After our first year we ripped out our furnace and installed underfloor hydronic and wood stove with the combustion air vented to the outside. An unexpected consequence was that our bedroom became more "stale" than usual in the heating months because we didn't have the air circulation from our forced air system.

To improve air quality and manage bathroom moisture issues we installed an 80 CFM bath fan controlled to run 50% of the time every hour. We never had a steamed up mirror again, but we had two problems:
1) Our bedroom air quality only seemed to improve if we kept our bedroom door open for good diffusion. I think it is very important to have fresh air in bedrooms (since that's where we spend most of our time) and I question how well exhaust only solutions typically deliver fresh air to bedrooms in real-life, especially in bigger homes than ours. Maybe someone here has a study to back me up on this idea?
2) We had to remember to turn off the fan whenever we opened our wood stove or we would have a room full of smoke. This was very annoying (and I suspect dangerous for some folks that could experience backdrafting issues).

I believe a balanced ERV system could fix both the wood stove problem and provide warm fresh air where we need it most. A builder's bottom line shouldn't just be about energy usage/cost (the ERV vs. PV question), but it also needs to think about how the house can adapt to the needs of all the future occupants. Also, I think ERVs could be installed for less than $2,000 in existing homes using the existing forced air ducting.

Dec 7, 2012 2:04 PM ET

Response to Brian Hludzinski
by Martin Holladay

For those who want the best ventilation system that money can buy, and who can afford to pay for it, you'll get no argument from me if you choose to install an HRV. The systems work great.

For those concerned about getting enough fresh air in bedrooms (sometimes a problem with exhaust-only systems), it should be pointed out that supply-only systems don't have that problem. The most common type of supply-only system is a central-fan-integrated supply ventilation system equipped with a FanCycler. Such systems are commonly installed on homes with forced-air heating systems (a type of heating system that Dr. Wolfgang Feist does not like, but one that is very affordable in the U.S.).

Like exhaust-only ventilation systems, supply-only ventilation systems are considerably cheaper than HRV-based systems with dedicated ventilation ductwork.

Dec 7, 2012 2:07 PM ET

Response to Kristopher Steege-Reimann
by Martin Holladay

Clearly, your choice of an exhaust-only ventilation system in a tiny house with a wood stove was a poor choice. Your backdrafting problems were predictable.

There is no substitute for whole-house thinking when it comes to designing a ventilation system.

Dec 7, 2012 2:24 PM ET

Edited Dec 7, 2012 2:33 PM ET.

Response to Brian Hludzinski
by John Semmelhack


Relatively poor distribution of outside air in most homes with exhaust ventilation is fairly well known, based on tracer gas experiments in "leaky" homes without passive air inlets. See for example -


However, in tight homes with passive air inlets, one study (from Sweden) showed satisfactory distribution of outside air. See - I'll be doing my own (less sophisticated) testing on an upcoming house and will try to report back the results.

Regarding comfort issues - I would argue that register location for any outside air distribution system (whether HRV or passive inlet) is more important than the delivery temperature. 65F air blowing over an occupant's skin is not comfortable. 10F air is, of course, even worse...but both can be mitigated with good register placement. High on a wall with a diffuser that throws air toward the ceiling and/or to the sides should allow good mixing before the outside air reaches the occupancy zone. Also remember - the airflows we're talking about for ventilation are really low...typically no more than 20cfm even for a master bedroom. For an example - see John Straube's presentation (esp. page 11) on the Dorset Street multi-family building in Waterloo - I wish I could have been at "Winter Camp" to ask him if there have been any comfort complaints.

Dec 7, 2012 2:52 PM ET

Fresh air distribution in homes with exhaust-only systems
by Martin Holladay

When it comes to fresh air distribution, at least one ventilation study (Robb Aldrich, Steven Winter Associates, Chicago, 2005) found that an exhaust-only ventilation system performed just as well as an ERV system.

A report on the study can be found online: . In that report, Robb Aldrich wrote, "According to the [CO2] histograms, it is the Air Cycler [central-fan-integrated supply system] and Exhaust systems that have the tightest distributions with the lowest CO2 concentration peaks. Table 2 confirms this, showing the Air Cycler system has the least variability in CO2 range followed by the Exhaust system; the ERV system has the highest variability. Because of the variability in occupant habits, however, SWA cannot definitively label a system as “better” or “best.” SWA can say qualitatively, however, that no system performed poorly in these homes in distributing fresh air."

Dec 7, 2012 3:52 PM ET

Edited Dec 7, 2012 3:54 PM ET.

Having trouble seeing the math on ERV vs vent.
by Ted Kidd

I like the climate charts! That's really helpful. But I'm having trouble parsing out the incremental cost/incremental benefit analysis. It does not appear clearly stated.

So, if I go to the total energy cost and see roughly 1000 KWH savings and call that $100 a year, then go to the $2000 incremental cost, I'll call that 5% annualized after tax. To me that looks like the increment pays, but to some it may not.

(Readers please note - having recently been faced with servicing a bunch of bath fans, the idea of one mechanical device has unfair bias right now.)

If we went South I'm thinking pretty quickly the increment won't pay, at least until you hit hot latent land. BUT once in that climate, cost benefit be damned I'm going ERV. I don't want a continuous depressurization situation. I'd be very afraid of rotting building components.

Dec 7, 2012 4:05 PM ET

Response to Ted Kidd
by Martin Holladay

The tiny air flows required for a mechanical ventilation system -- 56 cfm to 64 cfm in Semmelhack's study -- aren't going to rot anyone's envelope.

But if you prefer to pressurize your house, you could install a supply-only system for a lot less than an ERV.

Dec 7, 2012 4:39 PM ET

HRV ERVs and energy models
by Carl Seville

Thanks for the great analysis. Although I agree with the issue that HRVs and ERVs in many cases don't provide the roi to justify the cost, here in the south we try to avoid exhaust only ventilation to keep hot humid air out of the house and building cavities. One typical alternate is providing air through outside intakes into return plenum of hvac system with a mechanical damper and timer. In my experience these are costly, inefficient due to using hvac blower motor, and are often poorly installed. They also extract a penalty on the HERS index while ERV and HRV can reduce the index by several points. Whether or not this accurately reflects energy consumption is another discussion. Given the fact that most certification programs incent low hers ratings and problems with alternatives, I am, at least for the moment recommending ERVs to my clients.

Dec 7, 2012 5:11 PM ET

Exhaust ventilation in humid climates
by John Semmelhack

I came across an interesting tidbit of information on the topic of exhaust ventilation in humid climates during my research. Up until last year, the ASHRAE 62.2-2010 ventilation standard specifically restricted exhaust ventilation systems to no more than 7.5cfm/100ft2 floor area in the hot, humid climates (1, 2 and the lower portion of 3, I think), with the same restriction on supply-only systems in very cold climates. However, the 62.2 committee fairly recently (late 2011?) approved an addendum that removes these restrictions and included the following rationale: “The committee reviewed Section 4.6, “Restrictions on System Type” and decided the restrictions were not justified by recent field experience. There was general agreement that the problems in both hot/humid and cold climates were caused by specific and easily avoidable errors in envelope design that could not be solved by the system restrictions in Section 4.6.” While this quote is far from a ringing endorsement of exhaust ventilation systems in humid climates, it would seem to imply that as long as you "don't do stupid stuff" with your building envelope, a house with exhaust ventilation in a humid climate will probably not experience assembly failure caused by ventilation depressurization of the house.

Dec 7, 2012 5:28 PM ET

Edited Dec 8, 2012 6:14 PM ET.

Response to Martin Holladay
by Kristopher Steege-Reimann

You claim that when it comes to fresh air distribution exhaust only ventilation will perform just as well as an ERV system, but I still am skeptical because I believe that closed doors prevent fresh air getting to where it needs to be (and away from where it shouldn't be, like an unoccupied basement) and ERVs will tend to be ducted for better fresh air distribution.

For example, I've noticed that if I leave my bedroom door closed for the night there is a tendency for room to have noticeable body odor and more condensation on the windows than if the door is open (room doesn't get colder with the door shut with in floor heat).

Also, when doing a blower door test or testing the bath fan, you know that opening or closing doors can significantly effect air movement. In my life, I see this when I take a shower. If I leave the door closed I end up with a steamy mirror and if I leave the door cracked I get much better ventilation.

The bathroom humidity problem wouldn't be solved with a ERV, (I probably need to cut a larger gap at the bottom of the door), but I think it demonstrates that things like partition walls and doors can significantly affect how air is distributed through a house. Also, here's a link to a study about the return pathway of air with exhaust fans:

And a serious (maybe stupid) question: If an exhaust fan provides fresh air distribution through the entire home, then wouldn't you be wasting significant energy by providing fresh air to an unoccupied basement, especially in a single story home where a basement can be 50% of the home's volume? Or do basements need to have ventilation anyways?

EDIT: This is the post I was responding to. Didn't mean to mis-represent Martin: "When it comes to fresh air distribution, at least one ventilation study (Robb Aldrich, Steven Winter Associates, Chicago, 2005) found that an exhaust-only ventilation system performed just as well as an ERV system."

Dec 7, 2012 5:30 PM ET

How are the passive inlets
by Ron Keagle

How are the passive inlets detailed? It seems like if you had enough of them, you would get some heat exchange where the inlet comes through the wall. But that may be a hard needle to thread.

Dec 7, 2012 5:41 PM ET

a few thoughts... 1. if we're
by mike eliason

a few thoughts...

1. if we're going to talk about cost effectiveness of PV v. HRVs, then we need to be honest about full cost (subsidies, credits, maintenance, etc). there was a session in hannover on centralized HRV units in a PH having significantly lower maintenance costs over decentralized units, noting that there are other associated costs of mechanical systems other than initial outlay. also, john's cost numbers will change (significantly for some regions) if/when a carbon tax is initiated.

2. this HRV discussion doesn't hold as much accuracy when comparing to larger buildings (esp. MFH/institutionall/commercial) - where mechanical systems are routinely oversized, even without utilization of HRV/ERVs. i believe adam cohen discussed this topic at the PHNE event last month. the PH argument really needs to be spread beyond detached single family housing if its to really have any impact, because it's less costly and easier to achieve on larger buildings - which, by the way, tend to have higher EUIs (thus, PH = significantly realized savings).

3. i need to look back at my notes/conference proceedings, however there were several presentations on PH in warm/humid climates - and there were several locations identified as being appropriate for extract air systems over HRVs. 'happy climates' if i recall correctly (san francisco?)

4. utilization of passive vents in some areas can lead to health issues where there's poor air quality (so again, associated costs of system).

Dec 7, 2012 5:44 PM ET

Response to Kristopher Steege-Reimann
by Martin Holladay

You wrote, "You claim that when it comes to fresh air distribution exhaust only ventilation will perform just as well as an ERV system."

Actually, I made no such claim. In the article, I wrote, "Defenders of HRVs will probably ... point out that an HRV provides better comfort and delivers fresh air more evenly than does an exhaust-only system. This is undeniable."

In Comment #9, I wrote, "Getting enough fresh air in bedrooms [is] sometimes a problem with exhaust-only systems."

Dec 7, 2012 5:49 PM ET

Edited Dec 7, 2012 5:52 PM ET.

Response to Mike Eliason
by Martin Holladay

You wrote, "If we're going to talk about cost effectiveness of PV v. HRVs, then we need to be honest about full cost (subsidies, credits, maintenance, etc.)"

I agree. The cost figures used in Semmelhack's analysis were unsubsidized costs, for both HRVs and PVs. His conclusion that PV systems are a better investment than HRVs holds true for unsubsidized PV systems.

From my experience, HRVs definitely have maintenance costs over 20 years (filter changes and repairs). PV modules don't, but interters may. (My first inverter lasted 19 years.)

Dec 7, 2012 6:19 PM ET

Edited Dec 7, 2012 6:23 PM ET.

Response to Martin Holladay
by Kristopher Steege-Reimann

"When it comes to fresh air distribution, at least one ventilation study (Robb Aldrich, Steven Winter Associates, Chicago, 2005) found that an exhaust-only ventilation system performed just as well as an ERV system." That post was what I was responding to. I didn't mean to mis-represent you.

Dec 7, 2012 6:45 PM ET

General Response
by Barry Stephens

I was in Denver, and attended John's presentation. There are several flaws in the metrics of the presentation, and I am preparing a detailed response. There are also studies being conducted to address this entire discussion with DATA. It is data that is missing here. Modeling, modeling, modeling. What we think will happen. I also attended Robb Aldrich's presentation, which he made at the EEBA conference in September. That study also lacks complete data.

Martin, I would encourage you to attend a presentation coming up at the NESEA conference in Boston in March. Eberhard Paul from, you guessed it, Germany will be presenting on H/ERVs, and about IAQ in homes. He has done more study and data collection on the subject than anyone I know, and I think that you will find that his data and studies will have you re-think things. One study that he did concludes that opening windows is a better combined solution for IAQ and energy efficiency than using bath fans, even in cold climates.

More to come.

Barry Stephens

Dec 7, 2012 8:51 PM ET

A couple $200 Panasonic
by Curt Kinder

A couple $200 Panasonic WhisperGreen 80 CFM bath fans set to exhaust 30 CFM constantly at 4 Watts each is looking better and better!

Dec 7, 2012 10:28 PM ET

Watching out for perverse incentives
by Skip Harris

Amory Lovins talks about spherically perverse incentives & I think that you are doing us a great favor by looking at things that may make sense from one vantage, but be unproductive from another: not spherically perverse, but not spherically sensible either.

Dec 8, 2012 3:14 AM ET

What about a Panasonic ERV?
by Gordon Taylor

Talk about cheap and simple. But is it relevant? I'm looking specifically at the "Panasonic WhisperComfort - (ERV) 40/20, 20/10 CFM, 0.8 sone APPA04VE1," which is available at Wal-Mart for $353. Supposedly it can be a Spot ERV or a whole-house ERV, though I'm not sure how the latter would work. This is not an exhaust-only fan, obviously, and it supplies fresh air without an expensive ducting system. Used in a master bath, could it solve the problem of stale bedroom air (in a master bedroom, at least), while a separate exhaust-only fan could be mounted in another bathroom? I'd love to see some comments on this.

Dec 8, 2012 7:22 AM ET

Response to Gordon Taylor
by Martin Holladay

The advantage of the WhisperComfort is that it provides some heat recovery. The disadvantage is the fresh air is delivered to the same room that the exhaust air is pulled from.

Many people with small homes or apartments are perfectly satisfied with the WhisperComfort. I have also heard of larger two-story homes with one WhisperComfort on each floor.

While a traditional ERV has four ducts to the unit, the Whisper Comfort has just two -- an exhaust duct and a fresh air duct. That simplifies ducting.

Dec 8, 2012 7:44 AM ET

Response to Barry Stephens
by Martin Holladay

Like you, I welcome more data, and look forward to hearing more from any disinterested third-party researcher who presents good, solid data. I plan to attend the NESEA conference in a Boston.

GBA readers may be interested in the fact the Barry Stephens is the national sales director for Zehnder, a manufacturer of HRVs, while Eberhard Paul is the owner of a company that manufacturers or distributes HRVs. When we consider data, we need to look at it with a critical eye, and consider not only the numbers, but also the source of the numbers.

I mean no disrespect by pointing out these facts. But most of us pay more attention to a Lawrence Berkeley National Lab study than a study sponsored by Venmar or Zehnder.

Dec 8, 2012 10:13 AM ET

Response to John Semelhack
by Doug McEvers


My intention was not to diminish the work you have done on this, my speed reading missed some key points as usual. I agree with you, an HRV/ERV is not cost effective in moderate climates. When exhaust only systems are specified, I believe the passive inlets should be used in conjuction. Fresh air in bedrooms is a concern for me and I have doubts about a single bath fan without passive inlets supplying this. I believe the MN code for ventilation air for a house is 15 CFM per bedroom plus 15 CFM. A 3 bedroom house would require 60 CFM continuous.

As you stated, cold climates have special considerations and heat recovery ventilation pencils out. I had heard a few years back about some slab on grade townhomes in the Twin Cities with exhaust only systems being very uncomfortable and expensive to heat. The comfort isuue may have been due to poor air sealing and and an improper slab insulation detail.

60 CFM is a lot of fresh air and in a 7,500 hdd climate would take 116.64 therms of energy annually to bring up to room temperature. A 75% efficient HRV would save 87.5 therms on a yearly basis less the extra energy to run the HRV. With natural gas as the heating fuel the ROI is borderline in this climate, a better payback when heating with electricity, propane or heating oil. I do like having fresh air delivered to every room in the house via the HRV, we use remote timers in the bathrooms and eliminate the individual bath fans.

Dec 8, 2012 11:21 AM ET

Response to Mike Eliason
by John Semmelhack

Regarding PV cost - my estimate was very conservative - $4,500/kW with no subsidy. Current prices in my area for medium-sized systems (5-6kW) are coming in at $3,800-3,900/kW. The Germans are apparently installing residential systems for $2,240/kW! ()

Yes, my study was only geared toward single-family houses, and I modeled a relatively small (for us) house. For larger houses with higher ventilation rates, the economics will change. More ventilation flow = more energy savings from heat recovery. The unfortunate situation for designers of small, low energy homes on a budget is that the available high performance HRV/ERV equipment is oversized (max. flows of 200+cfm) and comes with a price tag to match. A hypothetical product with a peak flow of 100-120cfm (and a fan energy “sweet spot” of 50-60cfm), along with a reduction in price could make the difference in terms of economics for small projects. I mentioned this in my presentation at the conference.

In terms of bigger buildings – yes, the economics are different…in some cases drastically different. In commercial buildings with high ventilation rates, ERV/HRV’s can displace large amounts of cooling/heating equipment cost….enough to almost make them pay for themselves in upfront equipment savings. In these cases, it’s a no-brainer! In multi-family buildings, I think it’s a mixed bag. It depends a lot on occupancy density/airflow rates, and whether or not a central system with little/no occupant control is feasible. In condominiums, I expect owners would not be willing to give up control over their ventilation rates. In tenant housing – maybe it’s OK. There can be metering issues as well. For instance, in the multi-family housing in my area most units have their own electricity meter, which makes it harder to justify a central system.

Regarding outdoor air quality – this is an issue for any ventilation system, balanced, exhaust or supply. Yes, currently marketed passive air inlets have low performance filters, but I don’t see any reason why this issue couldn’t be addressed. Most ERV/HRVs also come standard with low performance filters. The only unit that I’m aware of that comes with a standard high performance filter is from Ultimate Air (MERV 12).

Dec 9, 2012 7:49 PM ET

Comments from Max Sherman
by Martin Holladay

Max Sherman, senior scientist at Lawrence Berkeley National Laboratory and former chairman of the ASHRAE 62.2 committee, sent me an e-mail with comments, along with permission to post his comments here.

Max Sherman wrote:

“Interesting discussion and I generally agree with you.

“In using the system that our passive friends want, you do not exhaust contaminants from bathrooms and more especially from range hoods. Cooking is probably the single most polluting activity done in homes and we do not want to recirculate the exhaust stream, we want to, well, exhaust them. Putting that air through an HRV (or far worse and ERV) means that a substantial portion of those nasties do not get exhausted.

“An HRV pulling from a bathroom is OK as long as it does not leak too much. An ERV pulling from a bathroom is going to recycle the moisture one is trying to exhaust and therefore most redistributes rather than exhaust moisture (and odors, etc.). The situation is much worse for the kitchen as the capture efficiency of the cooking contaminants is terrible without a range hood.

“ASHRAE 62.2 removed the prohibition against exhaust ventilation in hot, humid climates. The reason is because the small amount of mechanical ventilation (e.g., 40-90 cfm) is not going to make a wall rot unless the wall is made very poorly. Even with a balanced system half the wall is going to have some infiltration because of stack and wind effects.

“Joe Lstiburek was the leader of the removal of that provision from ASHRAE 62.2 because he says it’s about the wall design, not about a piddly amount of exhaust flow.

“Now, if you have a 1,200 cfm kitchen exhaust fan, as some high-end homes have, that is potentially another story, but nevertheless it [potential damage] is still about the wall.

“Passive houses can be so tight that they cannot manage even a reasonable amount of exhaust flow. This is a separate issue -- that their spec is foolish.”

Dec 10, 2012 3:57 AM ET

'Passive houses can be so
by mike eliason

'Passive houses can be so tight that they cannot manage even a reasonable amount of exhaust flow. '

granted, i'm not an LBNL scientist, but this is contradicted by all the literature and data i've ever reviewed, as well as personal experience visiting and staying in passivhaus buildings. quite the opposite, in fact. i've always been impressed at how clean and fresh the air quality is in a passivhaus compared to other buildings (especially commercial). RH appears to be more stable in a PH than in code built and existing houses as well.

in every comparison i've seen between a PH, code and existing building, the CO2 concentrations of the PH have been far better than others. here's one recently published from scotland:

monitored community center retrofit showed CO2 concentration at 750ppm or less 80% of the time, very little if any above 1350ppm.

i wish the PHI would translate their papers on monitoring rehabilitated projects because those are a minefield of data as well (and again, i've yet to see one project where CO2 concentration post PH Rehab is worse).

there is a developer of dormitories for foreign students in vienna that was so enthralled at how the moisture/mold and food odor issues that had plagued his previous buildings weren't an issue once he built a passivhaus. only building PHs now.

there have been a number of retrofits where the improvement from air quality in moving to passivhaus was so great, folks were able to stop taking medications they had been on for years - a number of different sources on this, most recent example i can think of are a few clients of bere architects (UK): .

this is where guenter lang's 'sex in a Passivhaus is safe sex' riff comes from.

also, is sherman thinking that range hoods aren't used at all?!? it's actually the inverse in much of europe, where ange hoods aren't the norm (and even in the US, recirc hoods are something like 80% of installations).

Dec 10, 2012 5:33 AM ET

Edited Dec 10, 2012 5:44 AM ET.

Response to Mike Eliason
by Martin Holladay

For the record, I agree with you on all the points you made.

I agree that Passivhaus buildings tend to have excellent interior air quality -- because of their tight envelopes and high quality ventilation systems.

I'm not sure, however, whether the publications of PHI are a minefield of data or a goldmine of data... perhaps both... Wade in at your own risk!

Dec 10, 2012 10:15 AM ET

Follow-up with Mike Eliason regarding multi-family buildings...
by John Semmelhack

In climates where clients are willing to forgo cooling systems AND the winter design temperatures are relatively mild (I'm thinking Portland and Seattle, for instance) the peak heat load in multi-family buildings with HRV/ERV systems can be low enough that ALL of the space heating energy can be delivered via the ventilation air (without increasing the ventilation rate!). This, of course, is the classic PH space heating strategy - high performance HRV/ERV, high performance domestic water heater tank, a small pump and a water to air heat exchanger to move heat as needed from the tank to the ventilation airstream. Maybe $8,000-10,000 installed for everything (ventilation, space heat and DHW)? These situations are where the economics start to swing back in favor of HRV/ERV, in my opinion.

On the other hand, this concept is much more difficult to achieve for buildings/clients that require space cooling.

Dec 10, 2012 3:21 PM ET

exhaust-only at cold temps
by Mojave Disaster, 3B

Martin Holladay wrote:

"The advantage of the WhisperComfort is that it provides some heat recovery. The disadvantage is the fresh air is delivered to the same room that the exhaust air is pulled from."

Another disadvantage, if we're discussing the ERV's advantage in cold climates, is the WhisperComfort's function as exhaust-only below 20F. "Frost-prevention mode." See attached image.

Screen Shot 2012-12-10 at 1.25.12 PM.png

Dec 10, 2012 3:47 PM ET

Response to Martin
by Barry Stephens

There will be a lot more data coming out on this subject shortly. The NorthWest Energy Efficiency Alliance has commissioned a residential ventilation study, and Washington State is doing the study. So your third party data and study is under way. I expect that 2013 will be a very interesting year for ventilation!

Dec 10, 2012 3:51 PM ET

Response to Barry Stephens
by Martin Holladay

That's excellent news. GBA looks forward to publishing new data on this issue, so you should feel free to e-mail me with any developments: martin [at] greenbuildingadvisor [dot] com.

Dec 11, 2012 11:21 PM ET

A few thoughts on HRV/ERV, IAQ and ventilation efficiency
by Brennan Less

First of all, HRV/ERV provide the least efficient spot ventilation possible. For example, when a shower occurs and a humidistat ramps up the unit to high airflow, the ventilation rate of the entire home is increased, rather than the ventilation rate of the room with the pollutant. This provides exceptionally low ventilation efficiency (mass pollutant removed/cfm). Similarly, kitchen ventilation using an HRV exhaust in the ceiling is not sufficient; once again, ventilation efficiencies are horrible. And even worse, essentially none of these systems ramp to high in response to cooking in the way they do to humidity events. My main problem with these systems is the belief that a kitchen range hood exhausted to outside can be eliminated if a fully ducted HRV is installed. The kitchen is one of the primary sources of pollutants in a home (especially one with low emitting materials), the bedroom is not. Even distribution of ventilation air is not necessarily desirable, rather you want ventilation when and where it is needed...and then some low rate for general purpose.

Dec 12, 2012 2:29 AM ET

Edited Dec 12, 2012 3:12 AM ET.

Local Superinsulation Club meeting
by Bronwyn Barry

I'm just catching up on this post now after a local Superinsulation Club meeting at the SF Elks Lodge. It took me a while because of the ball and chain I drag behind me. (Mine says 'made in the Netherlands' by the way Martin, because the Zehnder HRV's I've spec'd are actually Dutch.)

Great post by the way. You've knocked this one out of the ballpark. All that data included in the hypothetical study (by a Passive House postulate given at a Passive House conference) has scored huge points for the Superinsulation team. (And everyone should get exactly how Passivhaus and Superinsulation are so different by now.) It has me really thinking hard about spending $2K more on HRV's. All that fresh air I've been spoiling my clients with may be total overkill. I see now I could easily just spec a few alternates (made in China) that just suck. Wow. So much easier and cheaper.

It's so great to have you really nailing all the unexamined postulates of the Passive House movement too. It's crazy how those folks are all working so hard to build low energy buildings. I mean, high quality products that cost a bit more are so stupid. Nobody should want those. Not even folks who live in the richest country in the world who use the most energy per person, globally. It will be so good when everyone simply goes back to the way it used to be, in the 70's, with you SuperInsulated guys who created such good software for everyone to use. I'm sure it's still available everywhere. Cheaply. Isn't it?

Dec 12, 2012 7:16 AM ET

Edited Dec 12, 2012 11:19 AM ET.

Response to Bronwyn Barry
by Martin Holladay

Sorry to hear that the ball and chain are slowing you down. (The device on your ankle also appears to be making you a little bit grumpy, unfortunately. But at least you still have your sense of humor.)

Let's see where we agree. We both like superinsulation; that's good. We both believe that it's a good thing to work hard to help others build low-energy buildings; that's good. We're both a little worried about the fact that our country uses more energy per person than almost any country in the world.

You raise a new question: one of software. My blog doesn't really discuss the issue of software, but I'm glad you brought the question up. Back in the 1970s, the available energy-modeling software wasn't very good at all. PHPP is much better than anything available back then. That's why John Semmelhack chose to use PHPP to model the buildings in the study you dismissively refer to as "a hypothetical study by a Passive House postulate given at a Passive House conference." Actually, any time that anyone uses PHPP -- even you -- the results are "hypothetical." That's the whole idea behind modeling.

So, where is the disagreement? It appears to be the issue raised in this blog: whether it makes sense in all climates to pay an upcharge ranging from $2,023 (for an American ERV) to $3,273 (for the Dutch equipment you prefer) for a balanced ventilation system with heat recovery.

Here's my take: such as system shouldn't be mandatory. It should be up to the client to determine whether to spend that much for the upgrade. You appear to disagree with me on that point, evidently defending the Passivhaus Institut stand that these ventilation systems should be non-negotiable. Fair enough, I suppose. But I remain unconvinced.

Now I have to head down to the local Elks Lodge to have another beer with my superinsulation buddies.

Dec 12, 2012 1:04 PM ET

Balanced ventilation without HRV
by Ted Clifton

Great article, Martin, you have finally reiterated what I have been proving for years! I put together a spreadsheet a while back that does the calculations performed by Semmelhack, I have attached a copy hereto. There are a few calculations he missed: 1. The cost of money over time, and 2. The expected inflation of energy costs over time.
My spreadsheet does not include the inflation on energy costs, which would probably skew the results more in favor of the HRV, but when the comparison with more PV is made, the PV would clearly win every time. The cost of money is included, because regardless of how you spend it (HRV or PV), the cost will be the same.
What all of you seem to be missing is that there is more than one way to achieve balanced ventilation. We have been balancing our range hood with a powered HEPA filter for years, solving the air quality problems that an HRV does not. The HEPA filter puts fresh air directly into each bedroom, and the exhaust comes from the kitchen/great room. We use a slightly smaller range hood fan than the HEPA fan, to give a slight positive pressure in the house. This partially makes up for the occasional bath fan use. When the bath fans are running, the 8" inlet for the HEPA filter provides the make-up air, not leaks in the envelope.
Finally, Martin's most important point is being lost in the weeds. The most important point is that the dogma of the Passivhaus system (or any other system not open to innovation) is clearly a detriment to the development of the next generation of homes. We are producing net-zero-energy homes at a cost of less than half of what "passive homes" are costing in our area. In the process, we are also meeting the EPA's IndoorAir Plus standards. Our homes are using far less energy (before counting the PV) than the passive house system requires, without "super insulating" them.

Dec 12, 2012 2:49 PM ET

Response to Ted Clifton
by Martin Holladay

Thanks for your vote of confidence. As Mao said, let a hundred flowers bloom.

My intent is not to endorse the Carter Scott approach to building, nor the Ted Clifton approach, but simply to affirm that we need to choose our specifications according to rational principles rather than blind obedience to a system that resembles a cult or some type of religion.

Especially in light of the many different climates found in North America, rigid rules are unlikely to yield consistently good results in all climates.

Dec 12, 2012 3:16 PM ET

In Canada...
by Lloyd Alter

In Canada, where HRVs are required by the building code for every new house, you can buy decent ones for 800 bucks. I can't imagine doing a new home where you didn't have such a system, balancing the exhaust and the input.

Dec 12, 2012 4:23 PM ET

Ted's System
by Elizabeth Kormos


We are building a near passive house and I am interested in your HVAC system with the powered HEPA filter. What is your heating source and do you have AC? What is the brand of HEPA filter system. We are located in Upstate NY so I am wondering if we should or should not install the Ultimate Air??

Dec 12, 2012 4:47 PM ET

Edited Dec 12, 2012 4:52 PM ET.

Smack talk at the Elks Lodge
by Bronwyn Barry

Glad you saw the humor in my post Martin. There really is so much misinformation out there about how to build high performance buildings. My main point is that too few of us are doing it, so you may want to ease up on the Jerry Springer comments towards the folks on your own team.

No doubt there is plenty of B.S. out there, but it is not limited to the Passivhaus community. You've done a pretty spectacular job yourself here of building a whole argument based on incorrect info about Passivhaus: an HRV is NOT REQUIRED to build a Certified Passive House. However, it is recommended for most climates (yours being one of them.) Should you install one, you do need to provide a third party commissioning and balancing report to receive certification.

Now that we've cleared that up, the informative sections of your post are very interesting, but not substantiated by enough real data for my own taste. I contacted my friend at LBNL, Dr. Iain Walker, to see if he had any solid info on this topic. Unfortunately the only study that includes any real data related to this topic is limited to 10 deep energy retrofits all here in California. Here's what Iain wrote:

"The homes in our study tended to have ERVs - that have a major drawback because they recycle moisture into the home from the kitchen and bathroom exhausts. An HRV would have been better. The answer is complicated by the ERVs not being operated in an optimum way. For example, we found that they were not set up to deliver 62.2 air flow rates (usually operating at higher total flows than 62.2 required - so ventilating more and using more energy), or to exhaust enough air from kitchens to meet 62.2 (too little exhaust - really needed exhausting kitchen range hoods). Generally they used too much fan power that offset any possible energy savings.
My opinion is that they are really marginal in our climate and you need to make sure that they are installed well and the controls are set up correctly and you should provide additional source control - particularly in kitchens."

So, looks like the data so far backs up John’s premise that an HRV/ERV may not be necessary for the California Bay Area. It does not address other climates with higher temperature deltas. It also does not look at the efficiencies of these specific units, duct leakage, actual wattage draw and actual air exchange rates supplies. Ergo: The Jury is still out on this topic.

Iain did go on to say that LBNL would love to do a more extensive study but is limited (much like the Passive House Institute) by resources of both time and money. I hope that the study Barry Stephens mentioned earlier will shed more light on the subject. I also hope that we see a few new developments from the manufacturer community in the interim, and that the cost and complexity of these units improves.

Anecdotally, we (One Sky Homes) just installed a 'hybrid' version of the equipment options studied by John Semmelhack in our current Sunnyvale EnerPHit project. We eliminated most of the (expensive) supply ducting for the HRV and are dumping all the fresh air supply into the main living area. This large area is serving as a plenum for fresh air, heating and cooling. The 'plenum' space includes a Fujitsu mini-split unit to meet the home's heating and cooling requirements. We've then installed a Panasonic WhisperGreen fan to push fresh air (plus heating or cooling) to the bedrooms. Both bathrooms are direct extract vented to the HRV. Kitchen hood extracts directly to the exterior. The project is being monitored extensively, so I’ll let you know what the data says on how this system is working when we have enough to share.

Interestingly, when Davis Energy tested the Panasonic fan, it was drawing well over the 7 Watts claimed on the box. We adjusted the ducting to reduce the flow resistance and it then reduced the power draw on the fan. Logical, but only caught because it was tested.

All this is to say that a lot more work has to be done. Real data needs to be collected and those of us trying to figure this stuff out have to make sure that all our systems are tested and are working correctly. Getting all frothy at the mouth and telling people that they're wearing a 'ball and chain' is not helpful. Or polite. This is still a free country and nobody HAS to build Passivhaus (yet.) We, and our clients, want to. It is interesting and the PHPP is still the only modeling tool that has been calibrated (that I know of.)

So now that I know you and your buddies are still having fun at the Elks Lodge, I look forward to an update on this topic when the real data is available. Always good to hear (most of) the smack you and the 'oldtimers' (your description) come up with...

Dec 12, 2012 4:51 PM ET

Does cost per sq ft matter?
by Derek Roff

I'm wondering if a house's cost per square foot has any importance in the HRV vs exhaust only cost/benefit analysis. Running some naive numbers, an HRV might have a footprint of 10 sq ft, and construction costs on a passive house might be over $250/sq ft. So that could add $2500-$3500 to the calculated cost of HRV. But is an HRV system really adding 10 sq ft to the size of the mechanical room and to the whole house? And since a sq ft of a mechanical room costs far less than the average for the whole house, what price should we put on the space required for an HRV system?

Do you think the space calculation has any significance in this discussion?

Dec 12, 2012 5:17 PM ET

Edited Dec 12, 2012 5:22 PM ET.

Another response to Bronwyn Barry
by Martin Holladay

If the Passivhaus Institut is willing to certify a building that lacks an HRV, that's good news. Someone should tell them that they need to correct the errors on the website that indicate that HRVs are required. If the main websites of a well-known standard-setting institution include incorrect information, I can hardly be blamed for taking the websites at their word.

Like you, I'm always interested in more data. But the basics of the energy use of exhaust fans and HRVs is not as complicated or unsettled as you pretend. You wrote, "All this is to say that a lot more work has to be done. Real data needs to be collected and those of us trying to figure this stuff out have to make sure that all our systems are tested and are working correctly." But here in my corner of Vermont, we've been installing HRVs since the mid-1980s, so Vermont contractors have a 27 year track record to go on. There are no huge mysteries yet to be solved.

It's possible to screw up the installation and commissioning of any HVAC appliance, and you are correct that many exhaust fans as well as HRVs are installed very poorly and don't perform as they should. All the more reason to prefer simple equipment over complicated gadgets!

By the way, the calibration of energy modeling software is a routine part of energy software development. Some software developers do a good job of calibration, while others do a not-so-good job -- but it is simply untrue that "PHPP is still the only modeling tool that has been calibrated." But I nevertheless take off my hat to PHPP -- it's good software.

The big guns at LBNL when it comes to ventilation are Max Sherman and Iain Walker. Max Sherman posted a comment on this page, “Interesting discussion and I generally agree with you," while you quote Iain Walker as saying, "My opinion is that they [HRVs and ERVs] are really marginal in our climate and you need to make sure that they are installed well and the controls are set up correctly and you should provide additional source control - particularly in kitchens."

So I don't think your arguments in favor of HRVs and ERVs are getting a lot of support from researchers at LBNL.

Dec 12, 2012 5:46 PM ET

There are HRV's, ERV's and HAHR's
by Bronwyn Barry

Now you know this is a nit-picky community and not all HRV's or ERV's are built alike. Most of what is currently available on the market should more accurately be classified as HAHR's (Hardly Any Heat Recovery.) These units absolutely don't make sense to install because their recovery rate (some as low as 40%) does not offset the energy expended by their fan motors. Using a broad brush to disqualify all heat/energy recovery units is therefore simply foolish.

Dec 12, 2012 5:51 PM ET

Edited Dec 12, 2012 5:52 PM ET.

Response to Bronwyn Barry
by Martin Holladay

You're incorrect when you accuse John Semmelhack of using a broad brush. He evaluated the Ultimate Air ERV and the Zehnder HRV -- the two ventilation units that are most often specified by Passivhaus builders -- and he evaluated them using PHPP.

There was no "broad brush" inclusion of 40% efficient units in his analysis.

Dec 12, 2012 5:57 PM ET

Terrific article and
by Katrin Klingenberg

Terrific article and discussion, Martin! Thank you!

Dec 12, 2012 6:06 PM ET

Response to Katrin Klingenberg
by Martin Holladay

Thanks very much. I look forward to any developments by PHIUS that might lead to more flexibility in the specification of ventilation equipment.

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