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: