Combustion Air Requirements

   March 14, 2023      Bradford White

Why is it important to understand combustion air requirements?

Without the proper amount of combustion air, gas fired water heaters will not operate properly and can potentially be harmful.

Symptoms of lack of combustion air

  • Nuisance pilot outage
  • Back drafting
  • Tripping thermal reset
  • Yellow luminous flame
  • Soot/ carbon build up
  • Carbon monoxide
  • Discoloration at the bottom of non FVIR water heaters

Determining combustion air requirements

Confined spaces
A confined space is defined as a room having less than 50 ft. per 1000 BTU/Hr.
Reference National Fuel and Gas Code (NFGC), Chapter 9

Unconfined spaces
An unconfined space is defined as an area having 50 ft. or more per 1000 BTU/Hr.
Reference NFGC, Chapter 9

Requirements for installing a water heater in a confined space

Power direct vent/direct vent
A power direct vent/ direct vent water heater is drawing all combustion air from outside.

Provide adequate combustion air
Communicate directly with an adjacent enclosure or directly outdoors. If direct communication is not available, the use of ducting may be necessary.
Reference NFGC chapter 9 for formulas and requirements.