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Seeking Advice on In-floor Backup Heat (LP Gas)

Post in 'The Green Room' started by DenaliChuck, Jul 26, 2013.

  1. DenaliChuck

    DenaliChuck Member

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    I'm building a new, super-insulated house in Colorado and intend to heat primarily with wood. The house will be a single story, slab-on-grade, 1,400 sq ft, with stained concrete floors through-out.

    I need a very efficient, propane fired, domestic hot water maker that could also provide back-up heat using hydronic heat tube in the floor.

    What's your advice?

    Thanks in advance.

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  2. begreen

    begreen Mooderator Staff Member

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    If this is back up heat, why go to the expense and complexity of in floor hydronics? There are simpler ways to space heat with gas.
  3. btuser

    btuser Minister of Fire

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    I'd have to agree. The time it takes a slab to come up to temp would be an issue. 2-3 days depending on design. Are you heating the floor with a wood boiler, just certain areas with it or is just in case you don't heat with wood?

    I've been in a couple super-insulated houses and if I did it myself I'd want ducted air for heat/ac and for plentiful air exchanges.
  4. woodgeek

    woodgeek Minister of Fire

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    In floor radiant heat and super-insulated houses don't mix. If you get the floor slab warm enough to feel cozy, then it overheats the house.
  5. semipro

    semipro Minister of Fire

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    If you want to go hydronic, maybe baseboard instead of in-slab?

    A condensing gas water heater could be used for this as well as DHW.

    This would also allow for later addition of thermal solar for hot water production.
  6. Highbeam

    Highbeam Minister of Fire

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    Well now, that's a bit of a broad brush. With a super insulated house and radiant slab you won't feel a warm slab but the house will be warm. What's the goal? Warm feet or a warm room? The leakier the home, the warmer the floor needs to be to make up the loss. In no case will the slab be cold.

    Radiant slab heat mixes very well with a super insulated home. What doesn't work well is switching back and forth from an air heater like a woodstove to a radiant slab heater since the delay is huge.
  7. woodgeek

    woodgeek Minister of Fire

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    Stand by my assertion. The thing that folks like about radiant floors, the warm floor, is not compatible with any structure worth the label 'superinsulated'. BTUs point is also true, in the limit where the heated slab is a big thermal mass, in a superinsulated structure the timescales get huge and proper control becomes very difficult. IMO this is all textbook stuff.

    If you are going for aesthetics (no radiators or vents) run a loop around the perimeter only, and then maybe we can talk. The thermal mass and radiant area will be smaller. But if you put in wall to wall, you can have problems, and if you don't the floor in the middle may be uncomfortable (a 75°F concrete floor will feel cold).

    Somethings go together like PB and J, others like PB and herring.
  8. Highbeam

    Highbeam Minister of Fire

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    This assumption is false. The heating system heats. Warm floors are a benefit but certainly not the only reason people like heating floors and warm floors are not a requirement. I have insulated but unheated concrete floors in my home and they do not feel cold. I propose that the floor temp more closely matches the air temp as your insulation level goes up.

    That said, there are better ways to heat a superI house than with slab heat. That thermal mass makes operation very complicated and often will lead to over and under temping.

    Scorched air furnaces would be able to hold temperatures more accurately.
  9. woodgeek

    woodgeek Minister of Fire

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    It appears we agree.
  10. begreen

    begreen Mooderator Staff Member

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    Personal comfort is a subjective assessment. Concrete floors in winter often feel like they draw the heat out of the feet. It's a common complaint. Personally, after working on them for years I can't stand them. But that is just my subjective perspective.
  11. Highbeam

    Highbeam Minister of Fire

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    I'm coming around.
  12. Highbeam

    Highbeam Minister of Fire

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    I do believe the trick comfortable concrete floors is to insulate under them and then of course, have them inside the heated envelope of the home so that they gain and hold the temp. A cold, uninsulated slab in an unheated garage will not be pleasant to lay on for most. Even after heating the air.
  13. begreen

    begreen Mooderator Staff Member

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    The trick for me is to cover them with a thick pad and rug.
    woodgeek likes this.

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