Thread: Register for Makeup and Combustion Air

This is an example of a register that connected to a duct leading to the attic space intended for makeup/combustion for a furnace in this utility room. The register is of the type that is able to be closed - similar to an a/c register. Is this allowed? Or, is it required to be non-closeable to prevent people from inadvertantly cutting off the combustion air supply?

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Originally Posted by Matthew Barnicle

This is an example of a register that connected to a duct leading to the attic space intended for makeup/combustion for a furnace in this utility room. The register is of the type that is able to be closed - similar to an a/c register. Is this allowed? Or, is it required to be non-closeable to prevent people from inadvertantly cutting off the combustion air supply?

If it is for combustion air it needs to be calculated in its most closed state, which means "it ain't gonna do no good" and needs to be changed.

Is it for combustion air or for fresh air?

The register needs to be non dampered type, the attic ducts for combustion air also should have no screens on them.