should we put a masonry heater in the basement of our superinsulated house?
Hello! I was wondering if anyone would be able to give me some advice on a few questions.
Is it a good idea to place a masonry heater (specifically a Tempcast 2000) in the basement of a superinsulated home?
Will we have issues with heat transfering too slowly to the rest of the home, or chimney/backdraft issues?
Has anyone installed prefab masonry heaters before, and would you recommend it for DIYers inexperienced with masonry?
Does anyone know of specific issues with the Tempcast 2000 that we should be wary of?
The high initial cost of masonry heaters meant that we didn’t even consider one at first. But we found a Tempcast 2000 in our area in good condition and for a very reasonable price, so now we are reconsidering.
Background info: We are building an off-grid super-insulated home with passive solar elements on a pretty tight budget. We are in climate zone 6. The house is 2 storeys + basement, 800 sq ft/floor so 2400 square feet total. We have double-stud superinsulated walls so our heat loss calculation came out at 14,000 BTU/hr (17,000 if we don’t run the HRV). Available wood on the property is typically Oak, Birch, and Elm.
The house in question was discussed in this thread a little while ago (thanks again for the helpful advice!): https://www.hearth.com/talk/threads/system-design-for-off-grid-super-insulated-home.181616/
We had recently settled on placing a conventional wood stove in the basement. We had been considering a masonry surround for the chimney, largely to act as thermal mass for solar gain from the large south-facing windows, but decided to just go with a double-walled stainless steel all the way up (27′) and earthen floor on the first floor for thermal mass instead.
I know lots of masonry heaters are installed as central, main-floor showpieces or in slab-on-grade homes, so I’m uncertain if it would be appropriate for a basement and/or for DIYers on a budget. Appreciate your thoughts on this question!
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I will give your post a bump to see if anyone has input.
My recollection of previous discussions is that masonry heaters aren't a good fit for superinsulated homes. These units work best when they are fired up at the beginning of the heating season and then used continuously until spring. This lack of flexibility means they can quickly overheat a tight space.
The manufacturer does not provide any specs on BTU of the unit, but looking at pictures, it is way too big for a passive house. The masonry aspect does slow down the heat transfer, but what you end up with is something that takes a long time to get warm, then overheats the house.
You do need an electricity free backup heat in off grid house, usually propane wall heater is the easiest. An alternative would be something like this:
http://flatrockpassivehouse.blogspot.com/2017/03/a-wood-stove-in-passive-house-feeling.html
Keep in mind this still needs pumps, thus electricity, for transferring heat to a water tank. If you size your plumbing right and can install the thermal storage above the stove, you can get it to work with thermosyphon, which is a much better option for off grid.