Thread: Combustion Air

Had one today that had a 2004 Amana 92000 btu high eff. furnace. It was in a 3 foot deep by 4 foot wide closet off of the utility room. Had solid doors and was just vented to that closet only. Is there a certain size closet that this would be ok in or is it always wrong with solid doors? Thanks!

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Was there combustion air brought in from outdoors,and what did the rating tag say?

No air of any kind brought to the closet or furnace.

Assuming no other source of combustion air, 92,000 BTU requires 4,600 cu/ft of confined space.

For an 8' ceiling that's 575sq/ft floor space, or 25x23'

If there were louvered doors opening to a similarly sized confined space they would need to supply 92sq/in of net free opening, which would translate (for typical restriction factors) to 123 sq/in of metal louvers or 368sq/in of wood louvers.

For a 12' wide wood louver, that would be around 30" in height.

For comparison, a 4x4x8' closet supplies 128 cu/ft, which will support a 5,560BTU appliance.

Also, keep in mind that you have to count all the gas appliances in the space, for example a gas clothes dryers (each needs around 200 cu/ft for combustion in addition to make-up air) and water heaters.

I have a spread-sheet I set up to calculate these requierments, if you let me know the BTU's of all appliances, I can give you the total requirements.

Thanks a lot.