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Community and Q&A

House heating – new construction

user-7122242 | Posted in Plans Review on

We are building a 2 level house in Nova Scotia, Canada, Zone 6. Each level is 1000 sq feet. The first level is a walkout basement (2 bedrooms, bathroom, laundry room and storage). The floor is concrete and we plan to heat this level with hydronic infloor heat using geothermal. The second level is an open concept living and kitchen area plus a bedroom and bathroom. We plan to have a woodstove on this level and will use it regularly when we are at home. We are unsure of what other heat, if any, we need to install on this level. How much heat can we expect on the 2nd floor from the 1st level infloor heat? The stairwell is open at both ends. Running infloor hydronic heat or baseboards off the geothermal system seems like overkill since it won’t be on when the woodstove is going. Would a few electric baseboard heaters be the best solution? The house will be quite well insulated – R40 under slab, R 34 basement walls, R 24 upstairs walls, R60 attic. Any advice would be appreciated!

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Replies

  1. Bob Irving | | #1

    Theoretically it looks like a very good envelope, but the house must be tight - what are your plans for that?

  2. user-7122242 | | #2

    Wood clapboard siding, house wrap, wood sheathing (builder is old school), metal roof, interior and exterior rigid foam insulation on foundation, double glazed vinyl windows. Any heating thoughts for the 2nd floor? Thanks.

  3. User avatar
    Peter Engle | | #3

    With reasonably tight construction and those insulation levels, even a very small wood stove may overheat the space. The radiant slab on the first floor will certainly provide enough heat to keep the upstairs from freezing, though it might be a bit chilly.

    R40 under the slab seems like a bit of overkill, especially when you've only got R24 walls above grade. You might want to think about saving some money on the underslab insulation and putting a layer of rigid foam on the exterior of the house.

    Others here will probably point out that the geothermal system is pretty expensive for the total amount of heat you're going to need. Have you gotten any quotes yet for the geothermal system and plumbing?

  4. Walter Ahlgrim | | #4

    Unless someone does a set of room by room manual J calculation everyone is just guessing how the system will work.

    Hydronic in floor geothermal is the most capital intensive heating system imaginable and will do little improve the comfort upstairs.

    How many hours a day will you spend in the basement enjoying the warm floors? Or is that money better spent upstairs where you would benefit from it every day.

    Please take the time to find and read the article about wood stoves and high performance homes generally they are not a good mix.

    You may be far enough north to make triple pain window worth wile.

    How air tight will the old school builder make your home?

    Will you have a HRV?

    Walta

  5. user-7122242 | | #5

    We will have an HRV. Still waiting for final quote but was told geothermal would be in 20,000 range (Canadian $). Property will be dug up anyways to install driveway, septic, and yard space. Heating basement floors with wall hung electric boiler was the alternative. Geothermal installer said the payback time would be 5-7 years but this may be an overestimate. Thanks for the advice!

  6. user-7122242 | | #6

    Peter, Sorry made a typo. Basement slab is R20 not R40.

  7. Andrew C | | #7

    Geothermal is overrated.

    Disclaimer: I am not a builder, so my advice is free and worth every penny.

    That said:
    a) I like the description of your house, assuming that you use a rainscreen behind your wood siding and have sufficient overhangs.
    b) I agree with Walter, an aggressive Manual J calculation is required to move past the point of speculation.
    c) Knowing that one should never say never, you should never put geothermal into a well-built house with reasonable air-sealing and insulation. Costs too much, requires one-off engineering design and installation, and likely (by all accounts) to significantly underperform calculations. Other than one or two die-hard advocates, few that haunt the GBA website promote the use of geothermal. It can be done correctly, but it's rare, and still more expensive.

    Do you anticipate needing any cooling, or just heating? I suspect that a small-ish mini-split could take care of your needs for a lot less money than the geothermal, using an off-the-shelf system, assuming that you’ve got good air-sealing (target written into contract?) and an aggressive Manual J or equivalent to calculate heating and cooling loads.

    You left out an important detail: you plan to use a woodstove “when we are at home”. Are planning to leave for the day, generally, or go to some southern climate like Arizona or Windsor for the winter months?

  8. user-7122242 | | #8

    Andrew, Thanks for your advice. Yes, I'm quite sure the builder will use a rain screen. Rain and wind are an issue in this area and so the overhangs are 2 feet. We won't need cooling. Right now this is a vacation house used weekends only in the winter. However, we plan to move there full time in 5-10 years.

  9. User avatar
    Peter Engle | | #9

    Who exactly uses a vacation house in Nova Scotia for weekends in the winter? Not to be mean, but Nova Scotia is pretty rough in the winter. It's beautiful in the summer. though.

    OK, I guess I'm being mean. And I'm retiring to Vermont in a couple of years, so i guess I shouldn't make too much fun. Like everybody else has said. have a good manual J calculation done. That's got to be the starting point for any intelligent design of a HVAC package.

  10. user-7122242 | | #10

    Peter - An oceanfront house in Nova Scotia is quite enjoyable year round when it's only an hours drive from your city house. Summers here are beautiful of course but looking out at patches of snow on a deserted beach with roaring surf is pretty idyllic too! Anyways, thank you for all the helpful advice - Janet

  11. User avatar
    Robert Opaluch | | #11

    If your walkout level faces southward, the south side is longer than east and west sides, and you have more or larger windows facing south, and are not obstructed much by trees or other buildings, or some combination of these...your wintertime solar heat gains could be substantial. If facing north, very little solar heat gain. For details please see:
    https://lakesideca.info/blogs/dept/guest-blogs/quantitative-look-solar-heat-gain

    Double-glazed windows could be U=0.5 (R-2) or could be much better insulated. Although windows and doors take up a small amount of the building envelope, they often lose as much or more heat than walls/ceilings. Usually argon fill and "heat mirror" glass coating is a minor uncharge that can improve heat loss performance substantially (about half as much heat loss). You didn't mention but hope you are budgeting good quality windows (I'd guess Canada has better products than typical US windows).

    Heat will rise from the lower level to the upper level through the 1,000 SQFT ceiling/floor (about R-5) in addition to the stairwell air flow. Generally people using a mini split on a lower level report the upper level is heated okay, but not cooled so well; and a mini split on the upper level report the lower level is cooled okay, but not heated so well. (Same for other heat sources.)

    Like others commented, air sealing is very important. House wrap is a good step. I'd worry that an "old school" builder may not pay attention to the many details that can result in a fairly leaky home. Air-sealing details planned for sealing around windows/doors/mudsills/vents, connecting the wall air barrier to the upper level ceiling air barrier, attic openings and ceiling lights, etc? Geothermal is an expensive option, and like others I'd suggest putting the funds into air-sealing, window or insulation upgrades instead.

    If I remember correctly, the "5-10-20-40-60" rule of thumb mentioned various places on GBA refers to R-5 (U=0.2) windows, R-10 sub-slab insulation, R-20 foundation wall insulation, R-40 wall insulation and R-60 ceiling insulation for cold climates. (With hydronic in-floor heat, I'd suggest a higher sub-slab insulation than R-10, which you already planned.) Often I see "pretty good house" examples that don't quite meet the R-40 walls, as it can require difficult construction details to meet that level in wall construction, compared to piling on higher levels of insulation in the attic or sub-slab.

  12. Dick Russell | | #12

    I'm surprised that no one has questioned installing hydronic infloor heating for a house like this. A bare concrete floor won't feel warm to feet until its temperature gets to 78-80 degrees F. The heat loss from the building will be very low (if properly built), so with little way for the heat to escape, making the entire floor that warm would raise the room temperature to the upper 70s, which would feel stifling. Modulating the water temperature to keep the floor in the low 70s won't make the floor feel warm to bare feet, so why go to the expense of installing all that plumbing in the slab? Most often the advice given on this site is to skip hydronic infloor heating for a tight, very well insulated house, put the money saved into the building shell, and either wear slippers downstairs or install thin carpeting over the slab. A slab with R20 under it will be near room temperature and will not feel at all cold with just the slightest insulation between the concrete and skin.

    While geothermal may well be hard to justify economically, given its expense for most homes, there are some situations that can make it less so. I chose it for my own house eight years ago, and I haven't been disappointed. The house is superinsulated (which you should want yours to be), a new well was to be drilled for the house anyway, and water quality in the northeast (central NH) generally is of good quality. So I made the decision to go with geothermal, using the standing column well approach. Extra cost for the well to make it suitable for geo was minimal, and the heat pump was just a two-ton unit, minimizing cost of that. Distribution of heat is done by warm air through three zones of ductwork, so I get summer AC also. However, even with these circumstances, a couple of minisplit air-source heat pumps provide a low-cost and efficient way to heat a superinsulated house and ought to be considered.

    1. Mike Clarke | | #14

      Why on earth would you run a floor at 26°C (80°F). Hydronic systems are all about heating demand and proper design - unfortunately, not many are. As I have noted before in other posts, if a floor at 20°C (68°F) can supply the heating requirements at the designed temperature delta, then you probably won't have warm feet. Hydronic heating is not about warm feet, it's about superior comfort. Unfortunately, it costs a pretty penny to set up. But, if you want superior comfort, not "cold feet, hot head" like mini-splits, and you're prepared to pay, go for it.

      Further, if you intend to go hydronic, make sure that a parts manual and operation manual is included. Most of these systems tend to combine multiple different products and systems, and without manuals you'll have a more difficult time when it comes to selling the house.

  13. User avatar GBA Editor
    Martin Holladay | | #13

    Janet,
    I'm late to the party, but I'm going to reinforce what others have said. There are three things wrong with your plan:

    1. You don't want in-floor hydronic heat.
    2. You don't want a ground-source heat pump (a "geothermal" system).
    3. You don't want a wood stove.

    Except for that, your plan is fine.

    To read more about these three issues, see these three articles:

    "All About Radiant Floors"

    "Are Affordable Ground-Source Heat Pumps On the Horizon?"

    "All About Wood Stoves"

    A house like the one you describe can easily be heated with two air-source minisplit heat pumps -- ducted or ductless -- at a cost that is thousands of dollars less than the equipment you describe, without any of the combustion-air problems associated with wood stoves.

  14. T. Barker | | #15

    Can someone please explain to me how R40/R34 in the basement, but only R24 in the main floor walls makes any sense at all?

  15. Yupster | | #16

    Two more things to point out: You said R24 walls but didn't mention any exterior board insulation to eliminate thermal bridging. Please be aware that if you are just installing R24 fiberglass batts, which is very common in Canada, then the actual performance of R24 in framing 16" o/c is only R15, per NRCAN's calculations. You can find them here if you want to add up different wall combinations yourself to design a well insulated wall.

    Also, R34 in the basement walls would require almost 7" of XPS. It seems unlikely that you have that much foam on your basement walls, even inside and out. But maybe you do. My guess is you have 2" of XPS, R10, inside and out and then a 2x6 R24 batt insulated stud wall inside for drywall and electrical. That's an actual R25 performance. Just pointing that out in case your builder is misleading you or is confused on how r-values work himself.

    1. User avatar
      Dana Dorsett | | #17

      Yupster: Just petting one of the peeves here but,

      "...exterior board insulation to eliminate thermal bridging..."

      is describing the impossible.

      Eliminate the term "eliminate" in any discussion of buildings with framing & cavity insulation. Replace with "mitigate".

      A number of ICF foundations would come in at about R34 whole-wall. eg:

      The Logix Pro 2.75" + 2.75" with the optional D-Rv 2" EPS adder comes in at R34 whole-wall, with typical wallboard, siding & air films counted in (higher if up-rating the exterior foam to the 40F performance of EPS.)

      But we don't yet know for sure what Janet's basement wall stackup is.

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