What is combustion air?
Combustion air is a source of oxygen needed to burn fuel such as natural gas. Your gas-burning appliances cannot produce a flame without proper combustion air.
Why does a homeowner need to know about combustion air?
Recently we were in a home where the homeowner finished the basement himself. It was a 100% DIY project, and may I say, he did a great job. The project included closing in a small room where the gas furnace and hot water heater were located. At first we were concerned that he had not accounted for combustion air, until we saw the door to the “furnace room”.
The homeowner provided a way to get combustion air to he gas burning appliances by adding this louvered door to the enclosed room.
There are calculations you can use to make sure you are getting enough oxygen to your gas-burning appliances.
What if you don’t have enough combustion air for your gas appliances?
You need combustion air for two reasons:
1. Safety: A lack of adequate combustion air may cause deadly carbon monoxide (CO) to build up in your home. If it’s severely short of air, the negative indoor pressure can draw the CO back down into your house.
2. Operation: If your furnace is starved of air, it simply will not function properly. If you see yellowish flames, or flames that are not uniform and almost look like they are “dancing” your unit may need more combustion air. Also a sign of a unit that needs more combustion air is soot around the opening of the burners.
How do you calculate how much combustion air an appliance needs?
You should always consult the code requirements for your area. In general, there should be two openings between the room where the combustion appliances are located and the adjacent rooms that contribute to combustion air, one within 12” (305 mm) of the floor, the other within 12” of the ceiling. Each opening should have a minimum of 1 sq. inch of net free area for every 1,000 BTUs/hr
Here is a short video showing the enclosed area where a homeowner added combustion air while finishing the basement:
