Size of Exhaust pipe

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?

Most plans I see use  6 or 8" exhaust pipes.

Please advise, thanks
Dave

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.

2 inches is far fetched. I'd say.