Combustion air and venting

Need a little assistance with venting requirements for gas appliances. Focusing on the venting only, not exposed paper facing, flex ducts in garage, etc. Thanks gents…and ladies in advance.

  1. Is a garage considered a confined space for combustion air? I have a high efficiency furnace and natural draft water heater in a single car garage that does not meet the 50 sq ft/1000 btu.

  2. This water heater has a goose neck vent facing downward. I have never seen this application before and seems improper but I was not able to find anything specific on it.

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Improper venting - has to have 8’ clearance from sidewall. Combustion air should be fine. WH needs to be elevated at least 18".


Yes, the garage could be a confined space if it’s part of tight construction. Natural draft cannot vent via sidewall without fan assistance. How did you calculate the garage space to be a confined space?

It is not 50 sq ft. It is 50 CUBIC feet.

length x width x height = volume
Cubic feet is a measurement of volume.


What was the total BTU input of the appliances and what is the volume of the garage?

Without these numbers you are just asking for trouble by mentioning any deficiencies in your report.

There are at least four problems with the water heater one if which is the flue piping. Sure looks like a great time to involve a professional and let him sign off on the confined space evaluation.

Yes, my apologies. Typo, I know it’s cu ft. Thanks for looking out though :slight_smile:

Thanks. I called out the height already. The 8’ rule was confusing me. So it basically can can’t out the side if it sticks out 8’?

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`Thanks. Yes, I have the BTU’s. I was just not sure if the garage was considered confined or not. I was thinking it would be but I have had other inspectors tell me it isn’t. Just trying to get more input. I called the water heater out for multiple other issues. Just trying to know the confined space question for next time I run across it.

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No ones going to route it horizontally 8’ :wink: It needs to go up above the roofline at least 2’ where it can draft properly.

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You already know it wasn’t professionally done and/or permitted installation. Just say that in your narrative that the area was questionable as far as combustion air/confined space location or you couldn’t verify for sure and to have the professional making repairs figure it out and repair as needed.


Not in every jurisdiction. 2018 International Fuel Gas Code. The reference you have is for a chimney termination not a B vent. The OP has B vent piping from the appliance.


Not if FVIR.