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gas water heater combustion air

Jim Baird

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4 hours ago, Jim Baird said:

A gas fired water heater stands in a house's utility room that holds about 60% of the 50 cf per 1K BTU needed to meet code.

The room does have a central HVAC supply duct.

Does that supply duct negate the room as "confined space"?

Not per the IRC. 

The City of Portland used to have a citywide exception that allowed a supply duct to serve as a combustion air opening if it was big enough to do so when the HVAC blower was not running. The upshot is that the duct is never big enough. (It makes no sense to have a huge supply duct going to a small utility room - and a large utility room wouldn't need the added combustion air in the first place.) 

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Thanks for the reply.  This room is about 1100 cf but 34K water heater wants 1700.

My wag at duct size is 8", which would take 142' length to make enough volume, but the supply system does size up as you approach the equipment, so I am thinking a louvered door might be the best approach.

Gas water heaters are not very common around here.

Edited by Jim Baird
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