Knowing What Size Air Vent to Use for a Boiler

When installing or upgrading a boiler, it’s very important to know what size and type of venting system is required to properly and effectively vent the gases of combustion from the boiler. Boilers are categorized by vent category. There are 4 different categories of boilers and each type has its own requirements as to construction materials used in the venting systems. Vent sizing of boilers is determined in 2 main ways. The first of these is by observing the size of the flue on the boiler itself and the other is by reading the ANSI (American National Standards Institute) tag affixed to the front of the boiler.

Flue Sizing

The minimum size of vent required by your boiler will be determined by the size of the boiler flue. When installing a new boiler, you may not use down-sized adapters to adapt a smaller vent system to the flue. This means that if the flue opening on the boiler is 2.5 inches in diameter, then the vent pipe must be at least 2.5 inches in diameter, if not larger.

Read the Tag

The size of the vent piping required by your boiler will be determined by the type of boiler you have. Atmospheric combustion boilers will produce larger quantities of flue gases and thus require larger diameter vent pipes. Other types of boilers will require much smaller vent pipes.