Alright Thomas, you've convinced me to dive into the batch box research... I spent a bit of time over on batchrocket.eu, donkey forum, and exploring your links. You are probably right- it wouldnt be any more complicated to build a batch box than Matt's stove. So I'm considering it... Here are some questions.
https://batchrocket.eu/en/building#size includes info on stove sizing, which I'm sure you are familiar with. I was a bit alarmed when I put in my information to the calculator. The house we are building is 30x18 (540ft2), with a loft. I calculated the volume to be 166m3. Coldest temp we would see is -34C(-30F), (This is rare, but we'll stick with it for the moment). Since this is a new build, with 6" walls and rockwool, I put it at a 1.0 insulation factor (more insulated than the 10cm polystyren, but less than 37cm insulating clay brick). Result is 9kW loss, requiring a 230mm(9") or 250mm(10") diameter riser, with 2+ firings per day. Since a -30F day is pretty rare, only a couple days per year, I tried it with 0F to see the difference (This is still a cold day, but we have many more of them than -30). Result is 6.2kW, requiring 8 or 9" riser (or a 10" for fewer firings). This makes me wonder if the Walker Full Masonry Cook Stove would be way under powered for this build? His plans said it could heat 1200sqft so I figured I was in the clear... But maybe thats using much different values for temp differential and insulation?
That leads to the ISA for the bell. The published numbers here
https://batchrocket.eu/en/building#bellsizing appear to be maximums. So I assume its alright if the ISA is less than that? We have a limited
footprint for this stove. A quick calculation says I could go 57"x32" (this is about what we were planning for the walker stove) by 6ft tall and be just shy of the 101sqft ISA max for an 8" system. Thats about 2x as tall as the walker stove, and a big increase in mass. Which will keep our house warmer. But that leads to the foundation question.
With the walker stove in mind when we were planning the house, (The plans said to plan on around 2400lbs) my husband planned in floor reinforcements, but we did not dig a footer for the stove. If we need to increase the overall mass to make this thing really keep the house warm... We might have a problem here. The foundation is in (helical piles), but not the floor yet, so techincally we could still dig a footer when the ground thaws, but I think the septic line runs right through where it would need to go... I need to double check that but it could be a problem. Any suggestions?
And finally, my aesthetic question. About 50% of the joy of
wood heat is seeing the fire. I am wondering if there are any places in the core of a batch box where a viewing window can be installed, besides the door. I am not sure how I would orient the new stove if we change course. But there is a chance the door won't be able to face the sitting area, which would make me very sad. I know Matt put a viewing window in the back of the core of the full masonry cook stove, and I sware I saw a video of his a few years ago with a window in the side of the fire box. Is this possible with a regular batch box?
Thanks so much for your help on this. I am glad I am digging a little deeper to really determine what the best build will be.