Countercurrent Exchange

Very useful information coaledsweat. Thanks very much.

I also have an exposed masonry chimney of similar length. Plus I burn my stove in the neighborhood of 400* (stove, not stack)--so my numbers may not be too different, but I have no baro damper. Getting those numbers myself is not something I'd have ventured due to my love of heights

I see what you mean about the amount of heat to be recovered being small, and air-to-air being not very efficient means of transfer.

I do not know if it would be worth the expense and effort but if you insulated the exhaust pipe and brought the intake into the wrap wherever it enters the masonry flue side-ensuring that no exhuast gases get into the intake, I would think you could transfer more heat to the intake and retain more in the exhaust. But you are still presented with the problem of lower amounts of oxygen to combust the coal because of the elevated intake temperature, as well as the impact on the flue draft resulting from the atmospheric pressure problem that was created