1 90 or 2-45's

I was reading another post Smoke Rolls Out Load Door - Any Advice?. Will 2-45 degree elbows give me a better draft than 1-90? I have a top vent with about 18" vertical before the 90 & a "T" for the baro & then right to the thimble. Not to much pipe. Thanks.

I subscribe to the least amount theorey. The least amount of pipe, elbows, angles and thimble pipe. If you have a great chimney, it really doesn't matter if you have a few turns. A poor one can make life difficult.

I don't think it would affect it that much, I would think the straighter the pipe, the better airflow and draft, also, I read somewhere, that Elbows, TEE, etc.. add "XX" in equivalent pipe length. (ie. 90 Deg. Elbow is equal to 10 feet of straight run? or something like that)

Actually two 6" 45* Els would have slightly less loss than a single 90* EL. The cost however, does not make this worth it.

Forgot the ratios on the table, they are 1/4, 1/2 and 3/4 going down from the top row for d/D.