One of the most misunderstood components inside a boiler room is the barometric damper, which is used to control the draft inside a boiler. It is installed on boilers that use a Category I vent. To understand how the barometric damper operates, we need to understand what draft is. We all know that when air is heated, it will rise. When hot air from the boiler rises up the stack, it must be replaced by cooler air surrounding the boiler. This cooler air will push the warmer air up the stack, causing flow. This flow of air from the boiler up the stack to the outside is referred to as draft. It also is called “chimney effect.”
The speed or velocity of the flue gas draft is affected by many conditions such as temperature difference between the inside and the outside of the building, wind fluctuations, chimney height, burner firing rate and barometric conditions. It changes constantly.