UEP United Energy Services

The Importance of Combustion Air

For efficient and effective operation in your boiler room, every combustion system needs a fresh air supply. If the air supply is not consistent or pressurized correctly, this can cause major issues such as outages, soot build-up, carbon monoxide, and other operational hazards.

Quantity & Location

NFPA 54, The National Fuel Gas Code, provides guidance on how to calculate the required amount of combustion air, approximately 4-6 square inches of free area for every boiler horsepower. This is critical to ensure the optimal performance of your boiler.

Ideally there should be two permanent air supply openings (one high, one low) within the boiler room walls to allow for optimal ventilation. If possible, locate these openings at opposite ends of the room to promote mixing. These openings are usually in the form of architectural louvers and should be unobstructed within the boiler room and the exterior.

Free area is important!  Louver manufacturers will list the amount of free area as a fraction or decimal.  Multiply your calculated area by the manufacturer’s listed free area to determine the actual louver size required.


Not every boiler room has direct access to the outdoors.  In this situation you can duct a source of fresh air to the boiler room or directly to the boiler.  Many high efficiency, condensing boilers employ this method.  Keep in mind that this duct should be sized for minimum pressure drop.

Rely on a Good Combustion Fan

For optimal performance, consider using a combustion fan for precise draft control. A properly sized combustion air fan will eliminate erratic, inconsistent air flows and ensure safe and efficient operation of the boiler. Contact us today to learn more!