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Any thoughts out there on adding a damper to the exit flue on a RMH? This wouldn't be for choking down the burn but rather to block heat from escaping up the chimney when there is no burn. Would the mass of the damper affect the performance of the heater when it's open? Would adding a damper even change heat loss that much?

Manny, I've given it a LOT of thought as I stand outside and watch the heat shimmers escape my exhaust pipe, but, everything I've read says it's a no,no. Mainly due to the fact that trying to decide when to safely close it is the problem.
I HATE losing all the heat I've spent so much time and wood creating. Matt, what's your stance on this?

I'm pretty sure it would make a huge difference, but it does scare me. I think a good seal on the feed will do 80% of the same thing, with no chance of CO poisoning. The coaling stage of a burn produces a lot of CO( I think), so you'd want to be sure that there were absolutely no coals left before shutting an exhaust damper. That said, one of the master masonry heater builders confessed to me that he does this with his personal home heater. He too was very wary of it though, but used it when he was leaving the house for long periods.

Yeah, I agree with both of you guy's comments. I need a gadget. Truth be told, if I was home or awake I would be burning. The idea of letting the fire totally die out before damping just isn't realistic for me with a RMH. But dang, even with a tight feed seal I get some crazy cooling when the outside air is <0.

I just saw this, manny...

I could build you a gadget. I already have the plans finished. It uses photosensors looking into the burn tunnel, when the coals are completly covered with ash and not emitting enough light, it closes a lid over the feed chamber. I did that manually with my cabin RMH, to keep it from convection cooling itself all night, it made a huge difference. I would Never put a damper on the other end, because of the aforementioned CO problem.

Thanks, Oddmar. That is seriously awesome of you to offer. I cover my feed with a big rock and that's no problem. I was thinking a plug for the other end. I just deal with it, though. It seems to be ok. As long as I keep the fire going, I'm just fine.