Combustable air

Trane furnace high efficiency 13 years old. Basement was finished and there is no air vent installed at the walls or door to the furnace room that is maybe 10X10.

There is a small hole at the furnace cabinet but no space under the utility room door

Does this unit need a compustable air vent?


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Is that vent not a pipe within a pipe can not tell from the pic and if it is it is getting combustion air.

Usually on HE Furnace (90+) install, should have two pipes coming off of furnace one for intake air and one for exhaust. Termination to outside air (also special procedures).Picture seems to show only one pipe hook up (exhaust). Would check model number, go to Trane Site and pull the PDF file that covers the venting procedure for model.

If 80+ or less, (non self contained combustion chamber), then may need to refer to National Fuel Gas Code section on Air for Combustion and Ventilation.Other local codes may apply also.

Circa 94 - 96 installs called for 50 cu feet for each 1000 Btuh of input for all the appliances (furnaces, clothes dryer, water heaters, etc) in the space.this was designated an UNCONFINED SPACE.

Back then, on new installs, we were being required to bring in outside air thru pipe/duct down a wall to within 12 inches of floor adjacent to furnace for combustion air no matter if furnace was 90 or 80, the intake was being required (locally).

Images are of manufacturer definition of required combustion air requirements circa 93 - 96. May need to save them and open them in a viewer to enlarge images.

80+ or less installs (non self-contained combustion chamber)

National Fuel Gas Code section on Air for Combustion and Ventilation or applicable provision of the local building codes should apply to both 80 & 90.

Circa 93-96, we were required to bring in outside air and terminate down wall within 12 inches of floor adjacent to any furnace. Did not matter if space was considered confined or unconfined or if furnace was 80 or 90.

Definition back then from manufacturer requirement on an 80+ or less install.

UNCONFINED SPACE - An unconfined space must have at least 50 cu ft for each 1000 Btuh of input for all the appliances (such as furnaces, clothes dryer, water heaters, etc.) in the space.

If unconfined space is constructed usually tight, aire for combustion and ventilation MUST come from either the outdoors or spaces freely communicating with the outdoors. Combustion and ventilation openings must be sized the same as for a confined space. A minimum opening with a total of at least 1 sq in / 5000 Btuh of total input rating for all equipment must be provided. Return air must not be taken from the room unless an equal or greater amount of air is supplied to the room.


A confined space is one whose volume is less than 50 sq ft per 1000 Btuh of the total input rating for all appliances installed in that space. A confined space MUST have 2 permanent openings. 1 within 12 in of the ceiling and the other within 12 in of the floor. Different requirements then came into play depending on where one was drawing the required air from.

Images may need to be saved then enlarged in a viewer, to be able to read the text


I’m not sure “Trane” offers a “Concentric vent design” on their 90% + Condensing type furnaces. The type unit I think I’m looking at in your picture would typically use a Exhaust & Intake pipe system. At worst, any enclosed area must have external combustion air (High/Low) installed to the area of any Gas-Fired appliance (ie: Furnace, Water Htr, etc.).
I’m sure you are aware, but I can’t tell you the number of times I’ve seen piped Exhaust/Intake venting of the furnace, and no C/A designed for the non-sealed HWH operation. I mean the Co. Insp’s. miss it all the time.

This is a TUC x x x B series furnace. On the right hand side of the venter motor is a blower assembly for pulling combustion air pipe into the furnace. The furnace may be vented either with or without the combustion air pipe depending upon installation location. Recommend that HVAC company install the combustion air pipe to the furnace.

As to combustion air, when in doubt, give an opinion or a description of existing conditions, and then recommend that a specialist comment.