Atmospheric Vent Gas Water Heaters and Attic Installations

For all gas water heater installations, it is very important to have sufficient combustion and dilution air. This ensures safe and proper drafting of the exhaust products, promoting reliable water heater operation. In some applications, atmospheric vent gas water heaters are installed in attic spaces, posing unique challenges to combustion and drafting.

As outside temperatures increase, the need for adequate combustion air and attic ventilation becomes more critical. For reference, attic temperatures can reach 160 degrees Fahrenheit or more if not ventilated adequately. These temperatures can be achieved when outside air temperatures are only in the 90’s; even on a cloudy day.

While the pilot flame burns, it consumes available oxygen from air within the combustion chamber. The exhaust gases from the pilot flame rise through the combustion chamber and water heater flue, ultimately exiting the attic space through the chimney system. The “draft” created when exhaust gases exit the chimney system pulls “fresh” air into the water heater combustion chamber to support continued pilot operation and/or burner operation.

For the exhaust gases to rise through the water heater and chimney system, they must have a temperature much greater than their surroundings. Elevated attic temperatures make it extremely difficult, or nearly impossible, for the water heater combustion system to “breathe” properly. Without the ability to sustain the pilot and main burner with fresh air, the pilot flame will become unstable, and may eventually go out. When this occurs, the water heater will not produce hot water.

To minimize the nuisance of pilot outages, proper attic ventilation must be present or provided. There are a couple common methods that help control excessive attic temperatures. Ridge vents allow the natural convection of hot attic air to escape from the attic, which draws fresh air through soffit vents near the bottom of the attic. Mechanical attic fan systems are an option to control air flow in and out of attics—they typically cycle on and off as the attic temperatures rise and fall.

Undersized, blocked or improper attic ventilation may result in elevated attic temperatures and water heater outages. Consult your local construction and roofing experts for further information about proper attic ventilation.