I live in northern bc I am considering a thermal mass rocket stove. I really love the idea of them but I am concerned that there will be problems getting it to start when it is really cold out. I have heard from others that you have to feed them all the time and not let them go out or you will have a devil of a time restarting them starting at -10C. Did they just have a bad build or is this a real thing?
They can be difficult to start up in cold weather if the heater itself is very cold too. Try this http://batchrocket.eu/en/ for a batch rocket that would not be required to feed constantly. My J style rocket mass heater needs to be fed every 10-15 minutes, but only burns for an hour in the morning and an hour at night on the coldest nights which are as low as -20C. Once the heater has run and the mass is warm the heater will have a very easy time starting up. Again, the batch box heaters take the constant feed out of the equation and only need to be loaded once every 40 minutes or so.
It gets pretty cold in Montana where Wheaton Labs/Paul's place is, and I don't think he has any specific issues. Some people, when building their RMH put a small port near the chimney in order to light a ball of paper or something in order to get the draught going. Then they light the fire. If your mass has any warmth (and it should, from what I understand, if you have built it right and you have not waited for more than a full day between burns), then it should also create its own draw without needing additional help with draught, as above. Welcome to Permies, Brenda. I am also in Northern B.C. and have intentions of building an RMH as well.
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My 8" J style rmh is in a plastic greenhouse / studio and we keep it warm all winter. No fire at night from 10 pm or so till 6-8 in the morning and it will be 40+ F in the morning. Being an 8" once its going well , it needs to be fed every 45 minutes sometimes an hour. After starting I switch from small split wood to larger split wood or a 6" round with small wood around it. We do keep it going all day during the coldest times but never at night . Any properly built RMH will have no trouble relighting, AFTER it has been dried out and has been completely warmed up. The ones you heard about with problems must have had issues like super strong winds or not enough chimney stack.
For your use in northern Canada, I would think that a batch box design would be a slightly better way to go. Harder to build than a J tube but Peter van den Berg has made all his designs publicly available ( THANK YOU PETER) and he or somebody here at permies is always glad to help.
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Switching from electric heat to a rocket mass heater reduces your carbon footprint as much as parking 7 cars