The Purpose of Chimney Draft and Flow

A chimney’s main role in any home is for removing combustible products. These include smoke, carbon dioxide, carbon monoxide, and water vapor. For a chimney to successfully remove these byproducts from a heating appliance including a fireplace, furnace, wood or gas stove, boiler, or a water heater, two huge factors must work together – draft and flow.

What Is Draft?

Draft is the desire of a gas to move through a heating system, or in other words, draft is the suction that keeps the smoke from entering the living space. This is technically the pressure difference between the interior and exterior of the chimney.

To produce a draft, the chimney requires heat, which pulls in combustion air and makes the fire burn hotter. As more heat is delivered to the chimney more draft is created. A chimney that is properly insulated is able to make more draft with less heat as it helps to keep the exhaust hot.

What Is Flow?

The rate at which gases actually move through a chimney is a known as flow. This is the measure of the molecules of exhaust gases that move through the venting system per a unit time.

Poor flow can be a result of a restriction in the flue like a kink in a water hose. Often the culprit of poor air flow in a chimney is excessive creosote deposits, closed or plugged dampers, improper construction, or structural damage. A dirty chimney cap can also result in bad air flow as it is kind of like having a water hose nozzle closed.

A qualified chimney sweep should be able to easily determine the root of any draft and air flow problem to ensure that the air in your home stays clean as it stays warm.

Resources: The Wood Heat Organization, Let There Be Light, CSIA