Heating a Super-Insulated House

On the question of “how we should heat this house?” we’ve considered the complete spectrum of possibilities.  The thing with super-insulation and passive solar is that you don’t need as much heat in the first place.  With the passive solar design, we hope to gain about 35% of our heating requirement from the sun.  While this is terrific, it does make the choice of heating system a little more complicated.  With R50+ walls, an R80 ceiling, and an air-leakage rate of >1.0  ACH50 we didn’t feel we could justify capital intensive systems such as solar thermal hydronic or geo-thermal.  While these are excellent systems that can save energy and money in many scenarios, with our designs this would mean spending upwards of $30-40,000 to save a couple hundred dollars a year over simple electric baseboard heaters  (see http://greenedmonton.ca/mcnzh-heating-system for a really good discussion of this issue).  After considering that we will also have a woodstove, we quickly ruled out this expense.
The building code dictates that you have to have back-up heat in addition to a woodstove.  Given the insulation and performance of the house, it is arguable that the best choice from a cost perspective would be simple electric baseboard heaters.  But we were concerned about resale value (if we needed to sell for some reason), and planning for when we’re too old to cut, chop and stack wood.  I’m not a fan of forced-air heating, so we have decided on a self-installed hydronic infloor radiant system using a 94% efficient propane fired tankless water heater as the heat source.  We will also wire-in (but not install unless required) for baseboard heaters in the bedrooms.
I have to admit that I am not certain this was the best choice from a cost-return perspective.  In fact, I know of one local family with a straw bale house, wood-stove and radiant system – similar to what we have designed. Their house is also passive solar.  They have never needed to use the radiant system – they heat 100% by wood as well as heat from the sun with their passive design.  But I think installing the radiant is the best decision long-term because it will give us flexibility for future solar thermal or wood-boiler applications if energy costs continue to skyrocket.  Bottom line for us is that with concrete floors, you only have one opportunity to install radiant floor heat.  Using our own installation labour, the cost of this system will be under $7500.  And since we will also get our domestic hot water usage from the same source, we further eliminate the cost of having a $1500 high-efficiency water heater installed!
The tubing will be installed in about 10 days = photos to come.  For much more information see:
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4 Responses to Heating a Super-Insulated House

  1. Jim Merrithew says:

    John
    You might find Jeff Armstrong’s blog about his energy-efficient house interesting.
    This is a link to his installation of Radiant floor heating
    http://dacinternational.blogspot.com/2008/11/waiting-for-slab-to-come.html

    You can find the blog by Googling: “DAC International + Snye House”

    Jim

  2. Laurel Greenberg says:

    May I ask you what size wood stove you chose for your home? How many BTU’s? I’m building a super-insulated house in Western Mass; I have a lot of wood on site and like a wood stove, but my builder is concerned about overheating.

    • Hi Laurel –

      This is a tricky question indeed! I asked this very question on GREENBUILDINGADVISOR.COM and got varying responses. You may wish to check that info out if you haven’t come across it yet. Here is what we did :

      Back in November when it became apprarent we couldn’t live in the house without a heat source other than the sun, we purchased a Scan 10 – a fantastic little stove rated to heat up to 1100 sqft (i don’t have the btu rating but it is available on line). It was a dream to operate but the firebox is small. We chose it because in theory, it put out enough btus to cover our heat load. And it was fine until we hit some really cold weather in December – -17C cold for a week. In that kind of cold the Scan couldn’t keep up. I should qualify that – it probably would keep up it you fed the stove all day around the clock. But I found that to be a pain and even with this practice the house was cold if we were not there to feed the fire. And of courser, it gets colder than that here for a few weeks each winter, so we concluded the stove wasn’t big enough for us.

      So we returned the Scan 10 to our dealer and purchased a JOTUL 500 rated to heat 2000 sqft. (OUr house is 3000). We burned a Jotul 500 for 12 years at our old house so I knew it would put out the heat we needed. I think with any stove in a passive solar superinsulted house, you have to take time to figure our the best cycle to burn your stove. For instance, if I burn a fire in the morning on a day when I know it will be sunny, we will definitely overheat (27C). SO I don’t put a fire on those days – on occassion I operate a small 1000w electric heater to take a chill off until around 9:30 am when the sun kicked-in.

      So we went with a stove that was much bigger than the btus we required. This likely works for us due to the thermal mass of our floors (I believe one of the experts on greenbuilding advisor had concluded that the termal mass would even-out the overheating threat). This works fine for us and I never needed to burned more than 2 fires per day. We heated the house 100% through woodstove and solar this year, since we don’t yeat have the secondary heating installed. But to get the right stove for us, we had to buy and install 2 stoves to get it right. I installed them myself but we did loose a few nundred dollars by returning the first stove. It was money well spent in my books. Perhaps you could borrow a spare stove from someone and run it for a while before taking the plunge of purchasing and committing? A test drive like that would have been terrific!

      Good luck!

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