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Community and Q&A

Infloor heat in basement and/or HVAC plus wood heat

kaaset | Posted in General Questions on

I am building new in NW Wisconsin. Tight , well insulated, SIP walls and insulated basement but not passive house. My architect wants hot water heat in the basement slab and 1st floor bathroom floor.He also would like an HVAC system for supplemental heat and AC. I want a centrally located Tulikivi masonry wood heater on 1st level. House will be 2000 sq. ft. basement and one level above basement. No solar. My question is: How much heat is passively carried from the basement to the 1st level. There will be an open stairway to basement. Does radiant heat travel through the wood floors? I don’t really want to invest in an HVAC if I am paying for a boiler for the basement. I am sure the masonry heater will be almost adequate alone on the coldest days if adequatly fired. Should we abandon the in slab heat and just go with HVAC? I am considering an electric storage off-peak HVAC made by Steffes Corp. I am trying to stay away from propane so all would be electrically powered.

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  1. Expert Member
    Dana Dorsett | | #1

    It takes a significant temperature difference to drive a lot of heat via convection through an open staircase but if you kept the basement at 80F you might be able to keep it "reasonable" upstairs.

    Radiated heat from the floor in the basement is absorbed by the ceiling above, then re-radiated to the room above, but it's not very effective unless there is an even larger temperature difference. The R-value of the ceiling, joist cavity space, subfloor & flooring add up, all reducing the rate of heat transfer to something pretty tiny at low temperature differences.

    Basement heat loads of moderate to high-R houses are pretty tiny- you may be able to heat the slab and the bathroom with an insolated zone off the hot water heater rather than a boiler, and spend the boiler money on a 1-1.5 ton cold-climate ductless mini-split to supplement the masonry heater. All space heating mini-splits operate in cooling mode as well, and cool more quietly and efficiently than window-shaker AC units.

    All heating solutions start with the room by room, zone by zone heat load calculations though, and without that critical first step take any recommendations with a large grain of salt.

  2. user-2890856 | | #2

    Terrance ,

    It is d9ifficult to give sound advice without heat loss numbers and the like which Dana mentioned above . Do you have these ? Tulikivi W10 might be an option to do what your drawings call for . There are things that can be done to take care of the whole house in all seasons .

  3. GBA Editor
    Martin Holladay | | #3

    Your question raises many issues.

    First of all, "HVAC" stands for "heating, ventilating, and air conditioning." It can refer to a boiler or a furnace. It doesn't mean "a forced-air heating system."

    Second, I agree with you that it makes no sense to include three expensive heating systems (a Tulikivi wood-fired masonry heater, a boiler with a hydronic distribution system, and a furnace with ductwork) in one house.

    If you want a backup source of heat (for times when you aren't using your masonry heater) that uses electricity, why not just install ductless or ducted minisplits? That way you can skip the boiler, skip the furnace, and still get both heating and air conditioning.

  4. charlie_sullivan | | #4

    Do I understand right the architect's plan is to heat water electrically, and then pump that through the slab? If you want to heat a slab electrically, why not just embed electric heat in it directly? I'm not a fan of either system, but I think the electric is cheaper.

    As usual, Martin and DD have good advice.

  5. kshenefiel | | #5

    Terrance, I suggest giving the open stairway to the basement a second thought. I live in a house with an open stairway to a finished basement space and have been putting up a plastic dust barrier across the stairs for the Summer so I can keep the basement humidity under control. I ’m in New England the northern edge of zone 5a but the Summer weather is very similar to Wisconsin in both temperature and humidity. Windows are routinely open on the main floor and the basement stays several degrees cooler. With the stair left open mildew was a problem, and a dehumidifier couldn’t bring down the humidity to even marginal levels. With the stair closed of even minimal dehumidifier use can bring humidity down to almost winter like levels.
    There sure are some big fans of heat pumps on this website but from what I’ve read a Northern Wisconsin winter is really pushing the technical limits of even the most advanced cold weather air source heat pump. Why not use a single wood pellet boiler for the radiant floor heat, the domestic hot water, and a zone of base board radiators to supplement the wood stove on the main level? That way there’d be no concern of loss of heat output during a prolonged cold spell. A boiler doesn’t have any cooling capacity but for northern areas a dehumidifier or portable combination dehumidifier air conditioner will better address the actually climate control needs than a mini split.

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