Boiler is in workshop and I've insulated boiler to help reduce heat lost. I'm thinking of placing fan behind stove pipe to help heat shop. Will this affect draft and or is it worth the added electric to run fan?
The stack temperature on a coal boiler is relatively low, I doubt you would be able to scrub much heat from it. Chimneys need some heat to function properly anyway...if it were me I would probably just hook up a zone in the shop.