The Lack of Combustion Air: A Potentially Deadly Problem

We are excited to share this guest blog post from a trusted inspector, Glen Welch, on the Lack of Combustion Air


I retired with 30 years of service from the natural gas industry at the age of 55 and started Welch Engineering, which is a Real Estate Inspection and Testing Firm. During my career at Atlanta Gas Light Company, as an Engineer and District Manager, I investigated a number of explosions, fires and deaths.

Several of the fires and deaths were the result of a lack of Combustion Air needed for natural gas appliances to burn properly. The code requires 50 cubic feet of air per 1,000 BTUs of natural gas used in the room where the appliances are located. Most of the time this becomes a problem when rooms are finished in a basement. It can also occur in an attic when it is encapsulated with foam. Many times the required permit/county inspection has not been obtained and the work was done by a non-licensed contractor. The original basement probably had plenty of combustion air, but now that rooms have been added, the area with the natural gas appliances (which I usually call a Utility Closet) is now a confined space and the need for Combustion Air has not been considered.

Lack of Combustion Air can result in a fire and/or death.  In the normal natural gas combustion process the byproducts of combustion are heat, water vapor and carbon dioxide (CO2). Incomplete combustion of natural gas, due to the lack of required  Combustion Air, produces carbon and carbon monoxide (CO), which can be deadly. Carbon (commonly called soot) can build up in the flue, block the exhaust, cause flame roll-out and burn the house down — and we all know that carbon monoxide gas can cause injury/death.

As you will commonly see in my inspection reports, I usually calculate how much combustion air is needed and try to explain the problem.  Many times the BuildFax Report I provide tells the true story (that no permits were issued). The customer indicates in the disclosure statement that everything was done to code, but I’m telling you the real story and possibly saving someone’s life down the road.

Example:  The finished rooms in a basement has left a utility closet with a solid door and the utility closet  is 10’ x 10’  with a  9’ ceiling. Multiplying equals 900 cubic feet of air that can be used for combustion. The original unfinished basement was 26’ x 30’ x 9’ which  equals 7,020 cubic feet of combustion air available.  If the furnace uses 100,000 Btus per hour and the water heater uses 40,000 Btus per hour we have a total need of 140,000 appliance Btus per hour in the room. Multiplying 50 cubic feet x 140 equals 7000 cubic feet of combustion air needed for the proper/safe combustion of the natural gas appliances according to the fuel gas code. —– What did the unlicensed/non-permitted basement room finishing do?  It left only 900 cubic feet of combustion air per hour in the utility closet and the appliances need 7000 cubic feet of air per hour. Note that the original unfinished basement had 7,020 cubic feet (26 x 30 x 9) of combustion air for the furnace and water heater, which was just barely enough.

The lack of Combustion Air is a potential deadly problem.

I know this information is more than you needed or wanted to know, but please take away the potential seriousness of the problem.

Thank you for using Welch Engineering for your inspection services.


lack of combustion air

Glenn C Welch, Esq., PE.

President and General Counsel

Welch Engineering, LLC

1345 Bridgemill Avenue

Canton GA 30114

cell 404-514-4519

fax 770-345-2209

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