What is draft a measurement of?

Draft is a measurement of pressure in a flue vent. Specifically, it refers to the difference in air pressure which allows combustion gases to flow out of the combustion appliance and into the vent or chimney. A proper draft ensures that these gases are vented efficiently and that there is a sufficient supply of air for combustion to take place effectively.

In a building analysis context, measuring draft is critical to assess the performance of heating appliances, as inadequate draft could lead to dangerous situations, such as backdrafting, where combustion gases are pulled back into the living space instead of being expelled outside. Proper draft also helps in maintaining optimal combustion efficiency, which affects energy use and indoor air quality.