Passive Houses burning wood

A passivhaus or other zero-energy or superinsulated home like ours which is very tight (0.6 ACH50) presents some challenges if one also wants to heat the house with wood (instead of fossil fuels). We’re not … yet… BTW.

I know some will say that they are heating their home with solar-generated electricity (using a air-source heat pump powered by PVs let’s say) but… considered from a holistic/wholistic energy-use and green standpoint, it would still be better to heat with wood. Or even better, solar thermal. That way, the PV electricity can go to better use offsetting someone else’s electric appliance use, for which there is no alternative. In other words, if you have a more carbon-neutral way of heating one’s house, it seems like a good idea, no matter how energy efficient your house is. And whether or not you have solar electricity panels on your roof.

Even a point-source propane direct-vent heater like a Rinnai might be less source-energy / primary-energy intensive than an air-source heat pump depending on how cold a region you are in, due to the decreased COP in cold weather (which only works to undo the inherent inefficiency back at the power plant — fossil fuel plants are roughly 33% efficient, so if one figures on a COP of 2.7, you are just getting back to ~0.9 or the efficiency of burning propane directly.) The complications with this thinking is: 1) price fluctuations of propane and high prices/gallon for low usage, 2) You need to poke a hole in the house for the combustion-air-intake and the exhaust and heat will be lost, 3) site-electricity (via PVs) — and solar and wood — are interesting because one could be more self-sufficient / off-grid perhaps. Or ready to use an interesting new electricity source — perhaps the GreenUp / GreenStart options from your utility company. MA and CA are given the choice of supplier — you can choose a 100% renewable source.

OK, so back to wood and the tight house, sorry! :-) The problem is that with a VERY tight house, one wants to make sure:
1 – the stove gets enough incoming air for the combustion (direct vent pellet stove, for instance) Solved.
2 – it has been sized small enough so that you don’t overheat the house (too much). One can always open a window. So this doesn’t bother me much.
3 – Is the wood or pellet stove and flue well sealed? (this is the biggest concern)
4 – Does the energy-balance math make sense poking 2 holes in the house (for intake and exhaust)? OK, this is a concern too.

Some links of interest:
- House 2.0: Wood burning issues
- discussion at passivhaus.us including The Skyline House by Rachel Wagner
- Wood Stoves in Passive Houses – Strategies for Comfort (PDF)
- Heating a Tight, Well-Insulated House

One response to “Passive Houses burning wood

  1. Pingback: net zero in new england seems easy now… « Erik’s Blog