Combustion Air with 2 elbows

Can combustion air (properly sized of course) have 2 elbows to get below a triple joist? The length is just under 20’ total, about 10’ sits up inside the joists, then the 2 elbows drop it down to get under the joist, then continues into the utility rm. 12" from the ceiling.

Depends on the furnace. You would have to check the installation manual. Long sweep elbows generally add 10’ each to the “total length” of the run.

The local AHJ requires two elbows form a ubend 12" below the ceiling and 12" above the floor. His theory is that it keeps the home owners from plugging it.

The elbows in your situation would add the same “equivalence length” as the ubend. Should not be an issue.

Great thanks Jeff. How about one opening vs two? In the 2012 mechanical code book it has both 2 opening method and 1 opening method. I’ve heard from various people / resources no longer need two vents one on top and one on bottom, 12" from floor/ceiling.

Also one more question- is there a restriction on where the combustion air vents on the wall? I.e 12" from window or door opening, 4" from soffit etc… I thought that refers to direct vent only, not regular combustion air to outside.