Combustion Air

[Eric Smith]

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!

[Harry Janssen]

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

[Eric Smith]

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

[Michael Thomas]

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.

[Eric Smith]

Thanks a lot.