well when 100% of the energy going up the stack 10% is a whole crap load of recovery!
But on a high-efficiency heating appliance only a small amount of the heat goes up the stack.
Sure it's nice to be able to salvage some of that as electrical power. But as MattM points out,
you don't want to pull too much of it and make your chimney stop working correctly.
Monoxide poisoning isn't the only issue. Too cold a stack can collect creosote, followed by
a chimney fire when the accumulation finally ignites, which may destroy, not just your stack
or your stove/fireplace, but your house.
If you do want to salvage energy from the exhaust heat, peltier cells are a rotten way
to do it (unless you only want a token amount). I wouldn't try to homebrew a peltier-based
power scavenger. I'd only use them in a professionally-designed, UL-approved, integrated-
with-the-stove (i.e. something designed to power the stove's own needs) device or a
designed-for-stock-stacks add-on module.
(It would be interesting if somebody comes up with a heat-engine or thermoacoustic
energy scavenger.)
