Help!😩Smoke Billows in Room! NEW Majestic Biltmore 42”

[begreen]

The ovaling on the cap rim is not warping. It's just the flexing of the thin metal rim. The rim will conform to the roundness of the chimney pipe when attached. I came to the conclusion of negative pressure a while back and still think the restrictive cap design is not helping. This seems to have been proven by the test with it off.
Whether adding 4' of chimney pipe will overcome the negative pressure or not is to be determined. With 4 ft added the chimney will need 2 braces. one at 5' and one at 10'. If the chimney pipe is chased, then the bracing will be different. There it gets braced with the proper braces to the interior of the chase.

 

[Trevor Tahclep]

Now I understand why these products are not sold here in the province of Quebec.
I absolutely do not like that cap as it seems overly restrictive and needlessly complex to me.

 

[stoveliker]

I agree with the second part of the latest Majestic communication.

The first is then covering their behinds. There is nothing more fancy going on in chimney caps other than their impedance to air flow (unless you have one designed for high winds).
No venturi effects etc. Just "can the gas get out". It's a turbulent and/or diffusive flow (not laminar) and with varying wind and exhaust flows, that turbulence will be - turbulent. I.e. not consistent.
If one little bend is going to affect the efficacy of that cap, it's designed too close to the boundary of functioning. The safety margin is then too low and the cap sucks - and should be replaced by a newer one (without a larger range of operation, and thus less chance of exhaust going into the room - which is a safety issue too!).