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Q&A Spotlight

Ventilation for a Very Small Home

A clothes dryer raises issues in a tight, well-insulated home. What are the options?

Lunos fans are one option for whole-house ventilation. The through-the-wall installations are unobtrusive and quiet — the air vent is to the right of the wall receptacle. (Photo: 475 High Performance Building Supply)

Houses with very low rates of air leakage and heavily insulated walls and roofs don’t allow much natural ventilation. The whole point of building a high-performance house is to control the source and amount of outdoor air that gets inside.

That’s why designers typically include some kind of mechanical ventilation, often in the form of a heat-recovery or energy-recovery ventilator (HRVs and ERVs). But as LH has discovered, providing fresh air for a very small house can be a little more complicated, particularly when factoring in a clothes dryer that vents to the outdoors.

“When we built our little home (720 sq. ft., basically 2 main rooms) 13 yrs ago, we made it very tight and well insulated, but we did not take into account the need for makeup air,” LH writes in a Q&A post. “The first time we ran our dryer, we had air pulling in through the electrical outlets!”

LH’s solution was to leave windows open a crack, and to install a fan to pull outdoor air into the laundry closet while the dryer was running. Because LH lives in the Pacific Northwest, the fan brings in cold, damp air during the winter.

Although wall and ceiling space is limited, LH wonders whether an ERV is a possible solution. In looking over the options, however, LH finds that advice on this issue seems to be appropriate for larger homes with forced-air heating systems.

“One thing I would like to see on this site is more advice for those with small homes,” LH says. “Everything seems to be geared to having a forced-air furnace, which I don’t have. It wouldn’t make sense in a house this size, and I’ve never cared for the kind of heat they give.”

Ventilation for LH’s very small home is the topic for this Q&A Spotlight.

An ERV is probably not what you want

Even in the Pacific Northwest, outdoor air may seem cold and damp but it’s usually much drier than indoor air in absolute terms, Dana Dorsett responds. So pulling in outdoor air doesn’t create an indoor humidity problem. It will, however, create an energy and comfort problem.

One possible solution is to install an unvented heat-pump clothes dryer. Because it’s not exhausting a high volume of indoor, it’s not pulling in a high volume of outdoor air to replace it.

Further, Dorsett says, LH would be better off with a heat-recovery ventilator rather than an ERV. The two systems both incorporate a heat exchanger to reduce energy losses, but an ERV preserves some of the moisture content of incoming or outgoing air. An HRV does not.

“An ERV usually only makes sense in locations that have a fairly substantial latent cooling (outdoor humidity) problem in summer,” Dorsett says. “In the PNW the latent loads are almost always negative  even when it’s hot out. An HRV (sensible heat only) makes more sense in your climate.”

Consider Lunos fans

The ventilation standard published by ASHRAE (62.2) calls for about 40 cubic feet of fresh air per minute for a 720-square-foot, one-bedroom house and 50 cfm for a two-bedroom house, Dorsett notes. That’s about half or less the volume of air discharged by a clothes dryer.

“But,” he adds, “if half the dryer makeup air is coming from the HRV it’s still better than pulling it through the electrical outlets (which is an indication of leaky house sheathing, by the way).”

Building Science Corp. believes the ASHRAE standard is too high, he adds. It calculates the required ventilation differently, suggesting that a one-bedroom, 720-square-foot home should have about 22.5 cfm.

This suggests that LH might consider through-the-wall fans, an option that GBA Editor Martin Holladay also suggests. (Holladay also noted, “HRVs, ERVs, and Lunos fans are not makeup air devices. They are balanced ventilation systems that exhaust the same volume of air as they supply. Manufacturers of HRVs and ERVs usually state this fact in their installation instructions, noting that these ventilation fans should not be used as a makeup air source.”)

A pair of Lunos fans would provide adequate ventilation, Dorsett says, and  “would also provide a makeup air path for the dryer way better than what you have going now.”

Passive makeup air

Michael Maines has another suggestion: a Panasonic bathroom vent to exhaust air and a makeup air kit from Lunos that lets in fresh air when the building becomes depressurized.

This is a tactic Brian P. uses successfully. “We run one of our bath fans 24/7 at 30 cfm for a 1300+ sq. ft. house and that seems like more than enough ventilation,” he writes. “For a small place like yours, I think anything over 30 cfm would be overkill. Your best options might be something from the Lunos product line: either one pair of the E2, and eGO or two, or even their low volume exhaust fan (if you don’t have a bath fan).” The products are available from .

Brian P. installed four Panasonic passive air inlets in his very tight house to provide enough makeup air for the WhisperGreen fan running at 30 cfm. When the fan is boosted to 80 cfm, the exhaust fan will still depressurize the house.

“We initially installed 2 passive air inlets because the specs say up to 18 cfm, but that is wrong,” Brian P adds. “The reality seems like they are only capable of 10 cfm. The Lunos makeup air kits look nice, but 4x the cost of the Panasonic.”

Brian P. isn’t convinced the arrangement is the best idea in his cold climate because indoor air gets a little dry during the winter. “But,” he says, “it’s probably fine in the Pacific Northwest. If building again, I would go small HRV or consider Lunos.”

Lunos and other potential choices

Maines sees a gap in the market for balanced ventilation equipment for small houses, one that is currently filled only by Lunos.

Although well-made and energy efficient, the Lunos fans may be a problem for light sleepers when used in a bedroom, Maines says, because they turn on and off every 55 to 75 seconds.

“I don’t think Lunos would bother anyone in a living area, but inside a bedroom, sensitive sleepers can hear the fan change direction every 55-75 seconds (55 for thin walls, 75 for thick walls),” Maines adds. “They also put a hole in the wall, so if you have thick, cellulose-filled walls and triple-glazed windows, which block almost all sound, Lunos punch a hole in that envelope. I still think they’re great, just not for every situation.”

Other readers doubt noise would be much of a consideration, point out that other options are on the market.

Trevor Lambert, for example, doubts that fresh air would have to be brought directly into the bedroom in a house as small as LH’s.

“If it was really deemed necessary, I would still default to a small HRV with ECM motors,” Lambert says. “ has 5 speed fan controllers, so getting down to sub 20 cfm should be a trivial matter. My Zehnder’s ‘away’ mode defaults to about 18 cfm, and in that mode it would have to be completely silent in the room for me to tell if it’s on at all, or powered off from 3 feet away. Once I dialed it back to about 10 cfm. I literally can’t hear it run.”

Lance Peters says Panasonic makes two ERVs that are worth considering. One of them, the , has settings for 10, 20, and 40 cfm and can be installed much like a large bathroom fan. A second, the , can be set to cycle on and off if 50 cfm is too much ventilation. That unit can run as little as 10 minutes per hour.

Either of these would be “great choices” for a very small house, Peters says.

Maines adds that he recently spoke with a Zehnder America representative and was told that the CA70 has been discontinued, and the ComfoSpot50 was never available in the U.S. market.

Pros and cons of unvented dryers

The possibility of installing an unvented dryer might be appealing, LH says, but a little research has turned up mixed reviews.

“Long drying times, clothes coming out wrinkly, inability to lightly dry delicate items/clothes getting very hot, and frequent repairs are some of the complaints I’ve been reading about,” LH writes.

Brian P replies that he has had an for more than three years, without the need for a repair.

“I can’t say that wrinkles and drying delicate items have been an issue or something important to us,” he says. “We like it because it takes up less space than separate washer/dryer and didn’t require a big hole in the house for vent (and makeup air issues). Those benefits make it worthwhile compared to a normal setup. In your situation, it seems like switching to a ventless dryer (or combo unit) would be easier than making major ventilation changes.”

Lambert says his  does take longer to dry clothes and also is “pretty noisy.”

“If you can put it away from the living areas, it’s not an issue,” he adds. “We have it in our upstairs bathroom, and while I wish it were quieter, I wouldn’t trade it. A regular dryer isn’t exactly quiet either.”

Aaron Beckworth says he has had an LG condensing washer/dryer for about 18 months. He can program wash and dry cycles before leaving for work in the morning, a plus, and clothes come out feeling soft without a static cling.

But, he adds, there are some cons: “The dry cycle is very noisy. It’s not a constant rumble noise, but an intermittent ronking mechanical sort of noise. We are in a very small home. Therefore, we try to always start our laundry on our way out the door. Of course this doesn’t allow particular items to be removed between the wash and dry cycles. The clothes do tend to come out wrinkled, some more than others. Jeans are the worst!”

Our expert’s opinion

Here’s how GBA Technical Director Peter Yost sees it:

It’s interesting that in really small airtight buildings even “small” pressures — such as that created by a clothes dryer exhaust — can pose problems. As Joe Lstiburek is wont to say: no good deed goes unpunished.

Here are the options as I see them, with variables being cost, efficiency, efficacy, level of technology:

Ventless heat pump dryer: Ventless condensing clothes dryers have been on the market for quite some time, but I have heard plenty of user complaints. For example, here is a detailed assessment of the from an owner of a local Passive House-performance-level home:

“I haven’t been thrilled with the dryer. There is no setting that gets the clothes really thoroughly dry, so you can’t just leave it to dry and walk away. When it’s signaled that it’s done drying (extra dry) the clothes are still a bit damp. If you catch it in time, you can do a second extra dry cycle to get them actually dry, but if you don’t, then they mildew…

“Our motivation for not using an externally vented dryer was that we didn’t want to have to re-heat the makeup air, but I think the right way to solve this problem is to actually have the dryer pull the makeup air from outside, heat it, and run it through the clothes, rather than trying to do a closed-loop heat pump system. The closed loop system sounds good on the surface, but the results aren’t good.

“… It appears that Bosch and Miele finally decided the American market was worth pursuing. I’d be curious to know if these dryers perform any better.”

Hang-dry in the same space your new HRV is servicing: My wife and I like hang-drying our clothes, outdoors when weather permits and indoors when not. We have an HRV dedicated to our basement (our radon mitigation system), which acts as a dehumidifier in the winter.

I measured how many pints/pounds of water are left in a typical h-axis load of clothing — about 4 — and then measured relative humidity in the basement when we hang-dry a load. Our HRV easily exhausts most of that latent load and is considerably more efficient to run — even for many hours — than our conventional clothes dryer. I just bump the fan speed up to high (200 cfm; about the same as the clothes dryer…).

Admittedly, in your very small home, this might not be quite as practical, but maybe you can cycle your clothes-washer and hang time so that it does not interfere with household operations or hosting small parties…

And, OK, Vermont wintertime moisture content of outdoor air is likely on average much lower than almost anywhere in the Pacific Northwest. Maybe you would need to plan your clothes cleaning operation around upcoming weather, which makes it more like drying clothes in the summer.

Air inlets: The thing I don’t like about this approach is that all kinds of events can activate these inlets, especially in a small tight home. The thing about opening a nearby window is that it is event-based.

Do your laundry someplace else: You need a bigger, leakier, building in which to dry your clothes — like a laundromat or laundry service. Of course, I offer this with plenty of tongue-in-cheek, but just sayin’…

28 Comments

  1. Alan B | | #1

    I have the Whirlpool heat pump dryer, for over a year now.
    Clothes come out dry, no wrinkle problems.
    On normal its slightly less dry then a conventional dryer, i remember reading a test and they found it got clothes 98% dry while conventional got 99% dry. Not a huge difference and no mold or mildew ever.

    Pros:
    Saves some energy
    No depressurization
    Keeps heat indoors in winter.

    Cons:
    Takes 2-3 hours a load on average, some will be done in 1.5 hours but there is no rhyme or reason, the same load that took 1.5 hours this week will take 2-2.5h next week. Then a month from now it will do it in 1.5 hours again.

    Both filters are rather flimsy.
    Adds dust to the air and you need to vacuum out the lint frequently
    The secondary filter needs cleaning frequently, if its more then partially clogged drying time increases substantially. It recommends cleaning every 5 loads, i recommend every 2-3 and wash the foam core.
    Adds heat in summer.

    I bought the extended warranty but have not needed it so far.

  2. rdanomly | | #2

    I'd echo Alan's comments.

    My Whirlpool heat pump dryer is only a few months old. No real complaints from me either. Dry times are quite a bit longer for towels & sweatshirts. If you are stuck in the laundry room, it can be noisy. We've changed our laundry patterns a bit to accommodate occasional longer dry times. Rather than "laundry day" over the weekend, we try to do a load in the evenings after work. There are plenty other things to do while the dryer gently dehumidifies the clothes. And the clothes can be put away before going to bed. I can't say I've had any problems with wrinkles yet.

    I will say that the laundry room will warm up a touch and be a bit more humid as the dryer is doing its thing. Which, in the winter is actually nice. I'm anticipating a little more run time from the dehumidifier in the basement come summer time though...

    1. Alan B | | #6

      I didn't do any scientific measurements but i found no observable humidity increase last summer in the basement, the dehumidifier produced about the same amount of water before and after the new dryer.
      And this makes sense, the drier produces liquid water that goes down the drain.

  3. Jay S | | #3

    I like the Lunos concept but worry about the noise. They use fairly small fans located in the walls. The noise specs listed on Lunos' website are mostly useless since there are no details about how the measurements are made. I think I would rather go with a larger conventional ERV/HRV unit with the fan(s) located outside and then only run it for 10 minutes every hour or so rather than continuously. The big downside with that are the ducts.

    1. Sam Bargetz | | #18

      We do use lunos fans in our apartment with one fan being in our bedroom set on low speed (1 of 3) and it’s almost not noticeable. But we do live in Brooklyn with noisy ICE cars looking for parking spots outside 24/7...

  4. Quinn Sievewright | | #4

    Hello
    I'll be in a similar situation albeit no dryer. The building will be just 350sqft built with SIPS with two sliding doors. I'm thinking of having a bath fan linked to the shower light to remove bulk humid air while showering, then maybe a very low cfm fan in the bathroom or kitchen/living area that can be on constantly to ventilate the space in addition to a passive vent located behind the small wood burning stove so that any incoming cold air at least picks up some heat from the stove.
    This is a holiday cottage so it will not be heavily occupied and it also needs to be a inexpensive. That being said, perhaps just a regular bathroom fan and opening a window a crack when I need to would suffice! Climate 4c.

  5. Peter L | | #5

    I have a Blomberg ventless heat-pump dryer. So far so good. No issues. Yes, it takes longer to dry but if you plan laundry duties correctly, you don't have to worry. The clothes don't come out wrinkled or damp, just set it to the extra drying mode and they come out dry. 100% electric home and my electric bill is $55 per month. I even have a heat pump water heater.

    If only people had to deal with REAL problems like hanging laundry outside on a clothes line like I did years ago before clothes dryers.

  6. Scott Wilson | | #7

    I read through the original thread posted by LH some weeks ago and it prompted me to create my own thread on how to ventilate a very small off-grid house.

    I find it odd that so much careful study has been done for this thread (about a grid tied house) in so much that several products are mentioned. methods of installation are analyzed and debated as well as possible long term outcomes and yet for my off-grid home the best advice people could come up with is "crack open a window".

    Which of these many options are the most suited for off-grid?

    1. Malcolm Taylor | | #8

      Scott,

      Doesn't that make sense for a couple of reasons? The options available to off-grid houses are necessarily limited by the amount of power those houses generate, and the number of off-grid houses is minuscule compared to grid-tied ones.

    2. Trevor Lambert | | #10

      I can only speak for myself, but being unfamiliar with the power limitations and energy priorities in an off grid house left me unable to make specific recommendations. I suspect that was the case for many. It's not like there was a lack of discussion in the thread.

    3. User avater GBA Editor
      Martin Holladay | | #14

      Scott,
      If I remember correctly, I referred you to an article with advice on the topic. If for some reason I failed to do so, here is the link: "How to Design an Off-Grid House."

      Here is the relevant advice from that article:

      "An HRV or an ERV can use between 300 and 1,300 kWh per year. That’s a lot of electricity — more than most off-grid systems can handle. To ventilate your off-grid home, you have three options:
      • Open a window when the indoor air feels stuffy. This is the method I use.
      • Install a Panasonic WhisperGreen exhaust fan — for example, the FV-05VK3 (rated at 4.3 watts) — and connect it to a very well-designed duct system. Operate it as little as possible.
      • Install a pair of Lunos fans, each rated at 0.14 watts per cfm. One reason that this approach may be appealing to off-grid homeowners: these fans use 12-volt DC motors, obviating the need for an inverter. As with the Panasonic exhaust fan option, I advise off-grid homeowners with Lunos fans to operate the fans as little as possible."

  7. frasca | | #9

    “I think the right way to solve this problem is to actually have the dryer pull the makeup air from outside, heat it, and run it through the clothes, rather than trying to do a closed-loop heat pump system.”

    I would love to see someone build this. I also saw it discussed here:

    My favorite idea of Marc’s: “Using cold outdoor air in the dryer may degrade its drying performance. A solution would be to fabricate a concentric pipe-within-a-pipe to serve as both air inlet and exhaust. The inlet air would be warmed by the exhaust air, like a miniature air-to-air heat exchanger.”

    1. Trevor Lambert | | #11

      This doesn't address the energy penalty problem. A different hack I've seen on is to leave the intake alone but feed the exhaust through a filter and back into the house. Seemed sketchy to me, but upon reflection is that much different than the condensing option? I guess the volume of air going through the filter is much different, but the filter on my condensing dryer doesn't inspire much confidence.

      1. User avater
        Peter Engle | | #21

        Trevor,

        That's a very bad idea for two reasons: First, the moisture from the clothes ends up inside the house. As we've discussed many time on GBA, tight houses have problems getting rid of humidity. Adding more is not a good idea. And, second, if you have a gas-fired dryer, the exhaust contains the products of combustion including carbon monoxide. This is a good way to kill the family. Even without products of combustion, there can be lots of volatiles cooking off of laundry at high temperatures, including products of chlorine bleach and organics. I prefer to exhaust all of that outside. With a condensing dryer, at least you don't have the moisture and CO issues. If you keep the fragrances and other crap out of the laundry, the volatiles aren't too much of an issue either.

        1. Trevor Lambert | | #22

          I had never considered doing it myself, so I didn't think through what should have been rather obvious consequences. Thanks for the clarification.

  8. Scott Wilson | | #12

    Malcolm, it's not that there are less products suitable for an off-grid home as opposed to a grid tied home that annoys me, it's the implication that ANY product that requires electricity is beyond the capabilities of a solar powered system.

    As I noted in my thread, the Province of BC now requires that a ventilation system that runs 24/7 be installed in all new residential construction. I checked if that applies to off-grid construction, and it does. I have no choice but to install one.

    I would think in answering my questions about which products are the most energy efficient for off-grid construction people would naturally choose those products for grid-tied construction (who wouldn't want the most energy efficient product?) , but the issue of electrical usage for ventilation devices rarely comes up.

    1. Malcolm Taylor | | #13

      Scott,

      You may find these useful:

  9. Calum Wilde | | #15

    I'll add another vote for Whirlpool heat pump dryers. We went from an old top loader and conventional electric dryer to a Samsung HE washer and Whirlpool dryer. The dryer makes less noise than the washer, so while it makes noise, it's not excessive. Together the time for a load takes about 30 minutes linger than before, but a load is now about twice as much clothes. It's been a year now and the dryer hasn't given us any problems at all. Cleaning the extra filter 9npy takes a minute or so, not a big deal, especially considering with the increased load size we're still cleaning a filter just as often. I was nervous about this purchase but so far it's met or exceeded all of our expectations.

  10. Mathieugr | | #16

    Electric ventless dryers are the norm in continental Europe, and I've never had any issue with the one I used for 7 years before relocating to the US. When we bought a vented gas dryer 2 years ago, we initially wondered where the condensation tray was and how it could be emptied...

    In my experience, clothes (e.g. dress shirts, jeans and khakis, etc.) are wrinkled coming out of either a vented or a ventless dryer, and require ironing.

  11. Jeff Stern | | #17

    Another vote for non-vented dryers. We installed a condensing dryer in our PH completed over 5 1/2 years ago and have never had any issue. Numerous residential clients have installed heat pump dryers over the last few years and all seem quite pleased. Recent multi-family projects are all using non-vented dryers as well.

  12. Jeremy Good | | #19

    Adding to the Whirlpool heat pump dryer user reports, after about a year of use:

    Ours seems to over-dry with very large loads (that fill the 4.3 cu.ft. washer without stuffing). After multiple warranty service calls and replacement of all the sensors and electronics... it's about the same. Recently, I've started using the "Casual" (low heat) cycle with better results.

    I've been monitoring energy use for about 18 months and it appears that the heat pump dryer uses about 60% of the energy that the old electric unit did, about what was advertised, IIRC.

    One of the techs clued me in on a drying time adjustment for the automatic cycles. It's called "Customer-Focused Dryness Level". Ha. I think that may say something about Whirlpool company culture. Anyway, from the tech manual:
    -----
    NOTE: If the customer complains about the clothes being less
    dry or more dry than desired and the moisture sensor passes
    TEST #5: Moisture Sensor, step 2, the total dry time can be
    lengthened or shortened by changing the Customer-Focused
    Dryness Level from “1” (standard auto cycle) to a “2” (15%
    more drying time), “3” (30% more drying time), “4” (15% less
    drying time), or “5” (30% less drying time) auto cycle.

    1. In standby mode (dryer plugged in but not powered up),
    press and hold the DRYNESS LEVEL button for approximately
    3 seconds. The dryer will beep and “CF” is displayed followed
    by the current dryness setting on the 7-segment display. The
    factory default value is “1”.

    2. Pressing the dryness level button cycles the dryness setting
    between 1, 2, 3, 4, and 5 in that order, starting at the current
    setting. The new setting is displayed in the 7-segment display.

    3. With the display showing the desired dryness setting, press
    the START button to save the drying mode and exit to standby
    mode (the START button in this mode does not start a drying
    cycle). The result will be stored in EEPROM of the CCU and will
    be retained after a power loss
    -----
    Despite some frustrations, I'd buy it again. Sealing up that dryer vent was so satisfying!

    1. Alan B | | #25

      This is incredibly interesting. I usually just let it run a load but last time i needed something early and with 30 or so minutes left (before the cooldown) everything seemed dry so i was going to try less dry next time and see if that gets dry enough but saves energy. I will have to try this after i try that next.

    2. Alan B | | #26

      So i used the less dry option, clothes were damp and took about 1 1/2 hours so i will try your method next.
      How did you get a hold of the above quote?

      1. Jeremy Good | | #27

        I googled around until I found this:
        .pdf

        It's not my exact model, but appears to be the same in every way I've been able to identify.

        1. Alan B | | #28

          Sorry I missed your reply till i went to make this change by rereading your previous post.
          Thanks for linking that PDF, i never came across it when i did extensive research when buying my dryer so i owe you one
          It worked like a charm, i set it to CF4. Now i will try a load to see if its improved.

  13. Steven Valenziano | | #20

    Another option to deal with dryer makeup air issue: locate the dryer outside in a covered area. I realize this won't work everywhere, but it works here in NC.

  14. Robert Pinder | | #23

    Why do responders keep saying an ERV should be used? It is clear from the manufacturer's info and several responders here that they are not make-up-air units. Indeed, as mentioned, they need to be balanced which means they bring in exactly as much as they exhaust. This is a ridiculous issue that building engineers should have take care of years ago.

    As recently as 2011 we built three dwellings here in southern Ontario - no make up air means was called for by building dept (I guess it's just supposed to arrive by magic from somewhere) HRV's and, of course tight construction, were required and the residents suffer for lack of air. I just don't get it - turn on the bathroom fan, have the gas dryer running - THEN have the gas stove on and try to make some utility out of the range hood! Good luck, scary to think about where or what the make-up air might be or be coming from. I can certainly say the smoke detectors tell the truth about what's happening to the air supply!!!

  15. Evergreen Certified | | #24

    I'm about to start a ~730 SF home in the PNW myself and have been thinking about this issue. I want to add another point that I don't think has quite been hit on - not only is an HRV/ERV (+ Lunos) not designed to provide makeup air but when these devices are thrown out of balance (e.g. more outside air coming in than exhaust air leaving) the heat exchange core will gradually cool down and now your supply air is closer to outside temp ... defeating the whole purpose of the heat recovery.

    Now, maybe for the limited amount of time the dryer or range hood is running it doesn't matter that much?

    I am leaning towards using a makeup air duct with motorized damper that dumps the cold air right near the mini-split head so it can be re-heated.

    Has anyone ever wired one of those dampers to a range hood AND a clothes dryer?

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