Dampers for rocket mass heaters

Does anyone have any experience or thoughts on installing a damper to help with a cold start? I'm thinking of installing one on my build but wasn't sure if it's overkill or a smart thing to do and more specifically where to put them without getting in the way. The Wisner's touch on this only on one or two pages but not a lot of information out there.

A standard damper, to close off the chimney, would not do anything good for cold starting; but a bypass damper to let the exhaust go straight up the chimney instead of winding through ducts or bells could make a big difference in ease of starting the fire when cold.

The usefulness would depend on the specifics of your house and installation. If you get good draft even when the fire is cold, a bypass damper may not be worth the effort and complexity.

Hi, if your flue is high enough, like in our 3 storied home, and the draw of the flue gets enough pull, a standard flue damper (round disc inside pipe) should be installed after the upward bend. In our home, there's close to 5 meters of horizontal pipe with 4 bends including the upward bend and then there's about 9 or 10 meters straight up and out. In our setup the damper goes in the vertical portion of the flue/chimney, right after the last bend. We've only used it without the mass for now, the mass will be added coming warm season, but having operated like this I would hit myself in the head for not installing a damper honestly. I would say it depends a lot on your specific situation if you need one and place of installment should be put at a convenient location where most of the heat has been extracted for longevity of the damper (it also provides a cleaning port!).

Arguably, if you have a 1 story home and 3 meters of horizontal pipe, it could be considered an absolute waste of good money, and in such a case it would probably have more use for a bypass as has been mentioned, which would be more costly but might be a necessity for cold starts on a windstill morning.