Cat IV Venting

jim_15

Most new category IV gas furnaces are dual-rated for either a direct-vent or a non-direct-vent installation. When installing with a direct-vent configuration, the intake and exhaust pipes are supposed to terminate in the same pressure zone on the outside of the building. When installed with a non-direct-vent configuration, the exhaust is supposed to terminate outdoors, while the intake simply takes air from the furnace room. Sometimes the manufacturer advises placing an elbow on the intake opening to prevent debris from falling into the burner compartment.

Lately, I've been seeing what look like hybrid installations where the exhaust pipe goes through the roof, but the intake pipe terminates inside the attic. This is not a configuration that's described in any manufacturer's instructions that I've seen.

Clearly, the air in the attic and the air above the roof will be in different pressure zones, so this can't really be considered a proper direct-vent installation. Can it, however, be considered a proper non-direct-vent installation?

EBEBRATT-Ed

I have seen some horizontal intake with the flue through the roof as well

Every MFG is different and most all the codes I have read defer to the MFG. instructions. If it's in their manual you can do it.

I was just reading the instructions for a Goodman furnace that still allows ABS pipe for the flue....go figure.
The only PVC specifically approved for the flue that I know of is IPEX. Or polypropolene like Centrotherm

jim_15

EBEBRATT-Ed said:

I have seen some horizontal intake with the flue through the roof as well

Every MFG is different and most all the codes I have read defer to the MFG. instructions. If it's in their manual you can do it.

I agree. However, I've never seen a manual for a Cat IV furnace that specifically says you can do it this way. Have you?

EBEBRATT-Ed

yes I have seen that. if i find a manual i will post it. It is confusing .