It's best to look at any chimney draft problems from a practical standpoint, if there are multiple devices installed along the flow path that are specifically designed to impede and limit the exhaust flow, it's only logical that particular stove/chimney setup will display a lower draft, or possibly not enough draft, to successfully burn the stove with good results. The stove will become very sensitive to any drop in barometric pressure, because these devices are limiting much of the draft to begin with. Even if a fpd or baro device is completely open, the flap being vertical still presents a minor flow restriction to the stove, instead of a completely open pipe. In an internal combustion engine, people pay big money to port the cylinder heads and intake manifold passageways, just to get the engine to breath better and make more horsepower, and therein lies much of the added power over a stock engine. Gas flow is gas flow, controlled by the laws of physics. Likewise, installing multiple flap valves that close completely or partially in a chimney, is going to have detrimental effects on the stove draft- because by design, that's what these devices were intended to do. The stove may work ok or barely in a high draft condition, but if the draft falls off due to less barometric pressure, a stove set up like that, will tend to go out, or heat very poorly. I've seen a lot of stoves with no damper, with manual fpd's, and a few with baro dampers- the worst problem I've seen, is a coal stove with a baro that would not even burn, and constantly went out. The next worst setup I've seen, was a coal stove with the exit pipe angling down, to make it under the mantle of a fireplace chimney- that stove won't burn coal well at all, and only works with wood. Coal requires a strong draft to burn. Anything done to lessen the draft beyond the ignition point, results in a stove that won't burn or heat, and goes out. I'd rather have a stove letting some heat up the chimney, than one that keeps going out and won't even start. So there you have it.