We have encountered another interesting problem – we try to treat all the problems we encounter on this build as interesting! – and spent another unexpected few hours today, researching. This is with the wood stove or, more precisely, the flue / chimney for the wood stove. It could be a big problem, or it could be relatively easy to solve. We shall see.
The issue is this: We had assumed that we would be able to insulate the chimney where it exits the building with some kind of fire-resistant insulation material. However our installer says that the Ontario building code requires space around the chimney where it goes through each floor and the roof / insulation on the outside, and that there are no insulating products certified in Ontario with which one can fill this space. So, basically, we would create both a thermal bridge and a big hole in the envelope, all in one go. This would undermine the air tightness of the envelope and cause big problems for passive house certification. Both we and the installers are doing some more research but, as we see it now, we have 4 options:
1. Build a bigger masonry chimney through the house down to the first floor, which we can insulate.
Not many, apart from it being somewhat insulated and complying with code.
i) More expensive
ii) This might be too big for the space we have – it would end up taking up more of the little corridor to the upstairs toilet and bathroom. We certainly can’t put 11″ of insulation on, as on the outside of the house. We have asked the installers whether we could do this just down to the attic floor level. They are getting back to us.
2. Install the stove next to an outside wall, and put the stove pipe directly out through the wall into an external flue / chimney.
From my research, this is also what happens most often in Europe.
i) Apparently the stove pipe can be sealed and be in direct contact with insulating materials, whereas the chimney can’t. I need to confirm this.
ii) No need to cut any more large holes in interior CLT, and much easier to deal with a pipe going through the wall than the roof
i) If we just wanted a stove for heating the house, we could install the stove near to any outside wall we wanted. However as it’s a hydronic wood stove and mainly for water heating in winter, we have to install it fairly near to the tank system. If the stove needs to be very near to the tank, then we won’t be able to see it. That’s not ideal but not the end of the world. I will investigate how far the stove can be from the water tank to still work effectively etc..
ii) If we have to put the stove hidden in the utility space, then we will have to be very careful about exactly where it fits, in relation to the tank, outside chimney etc. We would also have to rejig water piping to accommodate the washing machine etc. (but which could even go in the pantry instead).
3. A more advanced technical solution that isn’t specified in the code
One such solution is made by the German company Schiedel,
(this is the UK site, which is in English, but they only sell directly in Europe).
It is a masonry-based chimney an integrated design. Apparently this is also used in passive houses in Europe. One version of their chimney also includes and integrated air intake for stoves that need it – and I am still not 100% sure if we might need external air intake or not, opinions differ and we need to talk to the HRV supplier.
i) Lack of certification. We would have to discuss any such route in consultation with our local planning officer, and probably have yet another engineer’s certification.
ii) More expense – including dealing with ports and import tariffs, overseas delivery etc.
iv) How insulated are these systems? We would also need to check the insulation rating etc.
4. Abandon the wood stove idea, ask for a refund and send the stove back.
i) Would save us all the problems of cutting holes in walls, inside and out, insulation issues, and everything else associated with the stove
ii) Would save us the costs of buying pipes and chimney, installation of all of these and stove.
ii) We can still use the rest of the water tank and solar thermal panel system.
i) Some expense (and effort) to send stove back
ii) We would have to use electricity for the supplementary / winter water heating until we work out something better, perhaps even going back to the currently inefficient, but in the future perhaps more efficient, use of Solar PV-generated electric.
iii) Need for a heating solution that the township is happy with – perhaps simple underfloor water heating would be enough. We could also investigate ground-source heat-pumps again in more detail again – we had abandoned the idea on ground of practicality (with the bedrock so close to the surface here).
iv) The stove supplier might not accept a return. We need to check.
We are currently leaning towards 2. or 4. (in that order).
If we can perhaps install the stove on the west side of the lounge then 2. would actually be pretty great. We would also have more space in the utility room…
We are still unsure what other passive house designs in Canada have done and are waiting for some feedback from our advisors. Watch this space…