I am planning on building a rocket stove heater using a 55 gallon barrel to heat my basement. Can I use an existing pellet stove exhaust pipe, its 4" and double walled?
If you build a 4" batch box system, yes, it will probably work fine. If you build a larger combustion core, it will depend on how good the draft of the chimney is. A really good chimney may be able to handle a core 1" or *maybe* 2" larger, but nobody is going to promise you that that will work well.
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