How to Properly Vent a Gas Water Heater

Use this article to find out how to properly vent a gas water heater and to safely remove exhaust gases to the outside atmosphere.

Good water heater vent is important for gas appliances to operate properly and safely remove products of combustion and water vapor out. To answer the question; how to properly vent a gas water heater, use the checklist below which provides the answers for:


How and where are you going to locate your gas water heater is very important, and if the gas unit is not properly vented heating performance will be affected or put your health in danger.

If you don't know how to properly vent a gas water heater, consult the local or national codes and manufacturer instructions, and keep in mind that combustion and ventilation requirements will determine where the unit will be located; is the area confined, unconfined or your gas water heater is located inside the small rooms and closets.

Confined areas are considered as areas with less than 50 cubic ft for each 1000 BTUH of the total input for gas fired appliances. Lots of air has to be provided for water heaters located in confined spaces or small enclosures. Two permanent openings are needed for normal venting, one 12" of the top and one 12" of the bottom of that enclosure. The size of the opening is determined by the total BTUH input of gas fired appliances inside that room.

If the air is supplied from the adjacent room, total volume of these rooms has to provide enough fresh air for combustion and ventilation.

If the air is coming from the outside, it can be transferred directly or using vertical and horizontal ducts, which should be with the same cross-sectional area as the free area of the opening.

For an unconfined space, or open area, an indoor air is used for combustion and the requirement for good venting is the minimum of 50 cubic feet for each 1000 BTUH of the total input of all gas-fired appliances located there.

Water heater vent system and air supply requirements are as described, very important so locate the heating unit as close to the chimney and venting system as possible. Venting system must be able to run from the water heater to the exit with the minimal length and elbows.

Tips on combustion air supply and ventilation

  • Proper clearances from the water heater must be maintained to allow the unobstructed air flow to the unit.

  • To properly vent a gas water heater, provide openings for air to enter and exit the area.

  • Openings for venting the gas heater, should be required size, per water heating manufacturer instructions and codes.

  • Fresh air should not be taken from areas where the negative pressure is, from areas where devices like exhaust fans, furnace, dryers or fireplaces are located.

  • Fresh air should be free of corrosive elements and flammable vapors. The warranty might be voided.

  • Venting pipe should be the same size as the openings.

  • Do not block with the insulation blanket or any other obstruction the base of the heater and draft hood, so the air can enter the heater chamber.

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Is vent pipe system discharging gases safely

Ensure that there is a proper drafting at the draft hood on the top of your tank type atmospheric water heater. If there is a problem with the correct venting check the following:

  • Is the draft hood properly installed?

  • Is the flue baffle positioned in the flue tube?

  • Is the venting system correctly sized?

  • Is the venting pipe system done per codes and standards?

  • Are all the vent connectors securely fastened and supported properly?

  • Any restrictions or obstruction in the vent system?

... to learn how to properly vent a gas water heater.

How to properly vent a gas water heater with a chimney connection

Chimney has to be clear and free of any obstructions and according to the codes, for the proper venting products of combustion. Chimney has to be certified for this purpose. How to properly vent a gas water heater? For the proper connection to the chimney follow the next requirements:

  • Install connector above the extreme bottom of the chimney.

  • The connection must be firm and sealed to prevent the vent connector from falling out.

  • Do not extend vent beyond the edge of the chimney.

Using vertical exhaust vent

Atmospheric gas water heaters with the vertical venting must be installed with UL listed type B vent pipe and according to the manufacturer instruction. Vent pipe must be terminated in a vertical position with a listed cap only, and it can be combined with the chimney as long as the proper draft is established.

How to properly vent a gas water heater? Recommendation is to follow codes, standards, manufacturer instructions and tips provided here.

For example, 90 degree elbow installed on the top of the water heater draft hood can reduce the vent efficiency by 50%. This is why it is important to allow a rise of ten vent diameters off of the top of the unit and before the first elbow.

Inspecting the venting system

Due to the Carbon Monoxide and fire hazard, inspect the venting system at least once a year. This is what you should check during the inspection and where to pay attention to properly vent a gas water heater:

  • Flue gases may escape if the vent pipe is not properly installed.

  • Sooted or deteriorated vent system causes the improper venting or leakage of venting gases.

  • Rusty flakes at the top of the heater are sign of the corrosion. Acidic water vapor or condensate is the cause of the vent rusting.

  • Remove the chemical substances as the vapor may lead to corrosion of the flue.


Another tip on how to properly vent a gas water heater is to check the draft in the water heater. Let the unit run for 15 mins put a match flame around the relief opening of the draft hood, and if the steady flame is drawn into the opening, this indicates the proper draft. If the flame flutters or is blown out, combustion products are escaping.

Water heaters are equipped with the thermal switch designed to shut off the gas supply in the event when the water heater is exposed to the flammable vapor or due to the poor combustion caused by the blocked vent or insufficient combustion air.

Common problems

  • If the heater is installed in a confined area and the burner will not ignite or burner flame is yellow, provide fresh air ventilation.