2.0204.1 Isolating Combustion Water Heater Closet

Combustion Safety
Desired Outcome: 
Isolate combustion water heater closet from conditioned space
Work assessment

Installer prework assessment will be conducted to determine:

  • Combustion safety
  • Proper venting
  • Structural integrity
  • Roof leaks
  • Insect infestation
  • Accessibility
  • Number, type, size, and location of penetrations

Ensure combustion appliance is functioning safely

Ensure work space is safe and ready for air sealing

Verify scope of work

Air seal closet

When the water heater closet contains a heater that is not sealed combustion or power vented, the closet will be isolated/separated from the rest of the home through air sealing with fire-rated materials, if feasible

Avoiding frozen pipes must be considered without creating an additional utility burden (e.g., heat tape)

Prevent combustion gases from entering living area and minimize extension of interior pressures caused by exhaust fan, dryers, and interior door closure into the water heater closet


Only noncombustible materials will be used in contact with chimneys, vents, and flues

Prevent a fire hazard

Post-work testing/verification

Blower door assisted zonal pressure diagnostics will be used to verify isolation has been achieved

Prevent combustion gases from entering living area