I have just finished my basement and my furnace is now in a room about 20 x 20. I had installed double doors (solid not vented) to enter the room which is also being used for storage.

My question is do I need to add some kind of makeup air for combustion by installing a grill in the wall? How do I know how large I need? Is there a way to calculate this? The heater is a 125,000 BTU york furnace about 2 years old.

Thanks for any help.

Next to the exhaust vent on the furnace, is there another vent connection? If so this is where a fresh-air vent pipe can be installed and piped to the exterior.
Air from with-in a building
"If the volume of space is greater than 50 cubic feet per 1,000 BTU/h....normal infiltration shall be regarded as adequate...
If not, 2 openings in a wall, with one 12" from the top & one 12" from the bottom. Each opening shall have a free area equal to min. 1" square inch per 1,000 BTU/h input rating of the appliance installed but not less than 100 sqr. Inches." (Internation Res. Code, section M1702.1 M1702.2)

If you have an installation manual for your furnace, it should tell. If not, go with the above rules. Those rules assume average construction. I actually tightened my crawl space up so tight, I had to add a vent for the furnace. I used the space between 2 joists as a duct ending it about a foot short of the furnace since the furnace was not set up for a duct.

Great - Thanks for the info, that's what I was looking for!

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Originally Posted by jimd60

I have just finished my basement and my furnace is now in a room about 20 x 20. I had installed double doors (solid not vented) to enter the room which is also being used for storage.

My question is do I need to add some kind of makeup air for combustion by installing a grill in the wall? How do I know how large I need? Is there a way to calculate this? The heater is a 125,000 btu york furnace about 2 years old.

Thanks for any help.

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125000 btu= 1.25 cubic ft... 1 cubic of natural gas require 10 cubic ft of air for a complete combustion... generally they use 50% excess of air... the min.excess air is 25%

If you want to make it real simple for yourself just add a vent to the supply and lock it open. The burner will draw combustion air from the register/duct system and when the blower is running there will be more air than needed. Code actually call for combustion air to be from a source that is 50% hi and 50% low is a enclosed room.