Furnace pulling combustion air from attic

[Trent Tarter]

Todays inspection had 90+ gas furnace (located in attic) that did not have PVC routed to exterior for combustion air and is pulling combustion air from attic space. Is this allowed? are there any problems with this other than being cheap and lazy.

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[Brandon Whitmore]

As long as it is a vented attic, I can't see why this would be a problem. The plus side is that it is one more roof penetration that the contractors can't screw up.

I don't see many furnaces in attic spaces, so I'd be looking into the entire installation as well.

[John Arnold]

This is a condensing furnace? How is the condensate handled? Could there be a freezing problem?

[Trent Tarter]

This is a condensing furnace? How is the condensate handled? Could there be a freezing problem?

With a condensation drain. Attic installations are very common here, I have never found a problem with condensation freezing. The only thing I am recommending on the combustion air part is to install a 90 degree elbow. Right now the combustion port is open on top of the furnace. If the evaporator coil ever leaked it would go straight into the combustion air opening.

[Jim Luttrall]

No problem with combustion air being taken from the attic so long as there is adequate attic ventilation. All furnaces in attics here use this method although we see very few condensing furnaces.
The attic is technically "outdoors" from a thermal and air boundary standpoint if it is a traditional vented attic.
Good point on protecting it from condensate leakage but again almost never an issue here as attic units tend to be horizontal applications.

[Markus Keller]

What's the attic insulation, loose fill or batt? How big of a unit, over or under 100K? Have them install a screen on the elbow to keep anything from falling in. Are there isolation pads under the unit or do you feel the vibration throughout the house?

[Craig Ervin]

Attic installs are everywhere here. The intake pulling from the attic is fine. The manual should be with the unit and you can read it if there are questions. Attics should be vented, thats another issue. Post a pic if you need a more detailed look. The is no more vibrations then a closet install. More noise seem to come from the return vent. They do make a fancy one piece flue intake that can be used if you don't want another hole in the roof. There might be a picture in the manual on attic installs too.