Combustion Air Requirements

Causes for Lack of Combustion Air

A house, which has been constructed tightly, often will not allow adequate air flow into the house for combustion. The problem is compounded by multiple air-using appliances, fireplaces and exhaust fans operating at the same time as the oil burner. A tightly sealed furnace room will create the same condition.

Another cause of a lack of combustion air is the environment in which the burner operates. If the burner draws air from an environment, which is laden with dryer lint and animal hair, the air openings, blower wheel and combustion head will clog, restricting the amount of air delivered to the combustion zone.

One of the first noticeable signs of a lack of combustion air could be the odor of combustion products in the building. In the case of a tight building with more than one air-using appliance running simultaneously, the building could be depressurized causing a backdraft in one or more of the appliances. This condition could cause flue products to flow back into the building.

When any type of combustion is deprived of the necessary oxygen, the correct ratio between air and fuel changes to a rich-fuel, lean-air ratio. This causes an oil flame to become lazy, orange and soot-producing. In the case of a tight building, a burner which is operating fine one minute might go into a smoky condition as soon as another air-using appliance is started. This can be detected by looking at the flame. However, the best test is to use a smoke gun and combustion test equipment to check the flue products.

When you are setting up a burner for the first time and the flame doesn’t seem to clean up, check for inadequate combustion air. To quickly find out if this is the problem, open an outside door or window and run the combustion and smoke tests again. If the flame cleans up, the problem likely is a lack of air. An audible sign of fuel rich combustion will be the sound of the flame. It will be loud and irregular. The reason for this is that the air and fuel do not mix properly due to lack of air. Not all oil droplets receive enough oxygen to complete the combustion process, resulting in an uneven burning of the fuel.

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