What do the air vents on a boiler do?

expert EXPERT April 26, 2007

Answer Air vents are sometimes called air eliminators. They can be manual or automatic, and their function is to get rid of air in the water. Boiler air vents are typically located at the top of the boiler. Automatic vents are often chromed and bell-shaped.

An air vent is not mandatory, although some boilers come with an integral vent. Some boiler designs are more prone to trapping air within the boiler than others. Most boilers with diaphragm-type expansion tanks have vents.

Air vents are more important on boilers with pumps. Pumps can be damaged by air pockets. Air vents are sometimes used with air scoops (air separators). These are devices built in to the piping system, designed to create an area of low water velocity so air bubbles can rise to the surface. They then usually escape through an air vent or into the expansion tank.

Conventional expansion tanks, located above boilers, can collect the air. Tanks with diaphragms (bladders) have no air/water contact, so they need an air vent. The bleed valves on radiators are air vents on the distribution side, although we don't call them vents.