How To Vent a Gas Water Heater

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Similar to a furnace, water heaters with gas burners will generate harmful fumes containing carbon monoxide, a byproduct of the fuel used to ignite the burner to heat the water in the tank, whether that fuel is natural gas, oil, or propane. Just like with your furnace, you need to have proper venting to exhaust the water heater’s toxic fumes to the outside of the home to keep you and your family safe.

What you need to know about venting a gas water heater

On standard gas water heaters, the fumes are commonly exhausted through a back draft insert and flue. The back draft insert prevents air from entering the top of the water heater and improves heat distribution in the tank. The flue is the venting that the fumes travel through to be safely exhausted outside of the home.

A water heater using atmospheric venting or direct venting will allow the fumes to exhaust naturally by rising straight up through a vertical vent which is routed to the home’s chimney, or through an upward sloping vent which may be routed through the chimney or through a wall to the home’s exterior. In both cases, the water heater needs to be located near an exterior wall or a chimney for the venting system to work properly.

On some gas water heater models, a power vent blower fan will be used to draw the exhaust fumes through the flue. Power venting water heaters are considered more energy-efficient than a standard direct vent system and are more effective at preventing back draft air from entering the water heater. Because the power vent uses a fan motor to draw the exhaust fumes through the flue, the venting can be longer and more horizontal which will give you more location options for installing the water heater.

Venting requirements

While you should always review local building codes to confirm the proper way to install water heater venting, here are some general guidelines to follow:

  • If your water heater relies on atmospheric or direct venting, you will need to use UL listed Type B metal flue piping that is three or four inches in diameter.
  • Water heaters with a power vent system can be vented using Schedule 40 PVC plastic tubing that is at least two inches in diameter since the blower helps cool the air passing through, although some experts believe metal piping is a safer alternative.
  • There should be a minimum of 12 inches of vertical venting between the draft hood outlet and the first elbow or connecter.
  • When using direct venting, any semi-horizontal piping should have a minimum upward slope of one quarter-inch per foot. The semi-horizontal distance should be no more than 75% of the total vertical height of the venting.
  • The venting pipe needs to be completely sealed where it passes through a wall or into the chimney to prevent air leaks.
  • When venting through a chimney, a UL listed chimney or vent cap must be used at the termination point.

Additional gas water heater venting information and safety tips

  • A direct venting system will pull the intake combustion air from outside the home (through the exhaust venting) whereas a power vent system draws in the room air that surrounds the water heater itself. For this reason, water heaters with a power vent should not be installed in small, enclosed spaces.
  • If space restrictions require the water heater to be installed in a utility closet, make sure the closet doors are louvered, or space left at the top and bottom of the doors, to increase air flow.
  • A power vent system may require the exhaust vent to be sloped to properly drain condensation that accumulates in the pipe.
  • Since gas water heaters use an open flame, keep combustible materials such as paint cans away from the unit.
  • Because there is always the potential for the exhaust fumes to leak from a gas water heater or furnace, one or more carbon monoxide detectors should be installed near the bedrooms of your home. The detector batteries should be checked regularly.

Find the right water heater parts with Repair Clinic

From power vent fan motors and pressure switches to burner assemblies and anode rods, Repair Clinic carries the specific replacement parts that fit your water heater model, including those manufactured by Rheem, A.O. Smith, Bradford White, Richmond, or Whirlpool. Type the full model number of your water heater into the Repair Clinic website search bar for a complete list of parts compatible with your unit. You can also explore Repair Clinic’s DIY content library to watch videos and read articles concerning common problems affecting water heaters, how to test certain components, and how to install new parts.

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