Combustion Air 1

[way]

I am designing a combustion air system for a residential home. The Mechanical room has appliances that total 573,000 btu/hr. The General Contractor has suggested that we place two openings (12"x12&quotin the mechanical room wall that will feed into a small storage room that will have one large louvered opening (18"x18&quotin an exterior wall (the louvers will be interlocked to the Gas Valves on all appliances). I have read through the Uniform Mechanical Code 2000 edition several times, and I can't determine if this is up to code. Any thoughts?

 

[superheat]

Assuming 2 horizontal vent to the outside, you need 1 sq. in of free space per 2000 btu. 144 sq in. will work for 288,000 BTU. The third vent does not qualify because they must be in pairs, one high and one low. If you plan on putting louvers or screens of some sort on those vents, the area will have to be increased more.
If those pipes are vertical to the outside, they will work for 576,000 BTU with no screens or louvers.
Your situation, i think, is venting from inside the building. Those 2 pipes are good for adding the space in both mechanical rooms to the your confined space calculation, 50 sq ft. per 1000 BTU. Vent to the outside from the second mechanical will not influence the inspectors decision in the least. The vent pipes must be permenantly open. Mechanically linked to the gas valve might work, but I would suspect the inspector would like to see an interlock. The louver is proven to open before the gas valve comes on.

 

[superheat]

After reading my post and rereading your post:
The outside vent would be the same as soffit vents in a house attic. I think that is 1 in. free space per 4000 BTU. Code still says permenant opening. You need to call the inspector on the louvers.
You need 2 pipes 17 x 17 with no louvers or screens for the combustion air into the mechanical room. You need 14,500 cubic feet in comunitation with your mechanical room to use 12 x 12 pipe. Do not forget to double required pipe area to account for an average grill.