Sealed combustion furnace in utility closet

I have a 60,000 BTU closed combustion propane furnace in a closet with 192 CuFt of volume. This does not meet the 50 CuFt/1000 BTU requirement. But, it does not take combustion air from the utility closet. It is closed combustion, with combustion air coming from the exterior of the building fed directly to the combustion chamber. Two PVC pipes are present; combustion air and exhaust air.

Does the 50/1000 rule apply here?

No it does not.


High efficiency furnace. @bcawhern1 has it right.

Just for clarity for anyone watching. Had the combustion air come from anywhere other than outside air, then the rule would apply.

Rule applies here because the combustion air comes from the interior.


Yep, and also for those watching, you should not refer to it as a “direct vent” furnace when set up as in Brian’s picture. In order to be “direct vent,” it MUST pull combustion air from the outdoors. That goes for all gas-burning appliances.


And if the combustion make-up air is coming from the interior in a closed utility room, louvered door(s) and/or permanently open louvered vents will be required, one about 12" off floor and one about 12" from ceiling, size of vents determined by calculation as previously mentioned. Same thing applies to fossil fuel water heaters.