Gas Water Heater Installation Instructions and Tips

Gas water heater installation instructions. A step-by-step guide on how properly to install a gas water heater, including tank-type water heaters from Rheem, Bradford White, AO Smith, Reliance, Kenmore, GE, American, and other manufacturers.

To provide years of safe and trouble-free service, installing a gas water heater should be done by the professional plumber or HVAC technician and following the codes (local, state and National Fuel Gas Code).

When installing a gas water heater, the manufacturer's instructions should be read carefully. The improper setup may result in inadequate performance, reduced efficiency, lack of hot water, shorter unit life, property damage, and health hazard.

How to install a gas water heater – Things to consider

Tools required

For the correct installation of the tank-type gas water heater, you should consider using the following tools:

  • Pipe wrench
  • Screwdriver
  • Drill
  • Teflon tape or pipe sealer
  • Hacksaw for cutting the copper pipes or tubing cutter
  • Propane tank and the torch
  • Tools for sweat soldering such as soft solder and wire brush
  • Expansion tank
  • Metal drain

Before installation, always inspect all the components inside the heater's box for possible damage. If something looks suspicious, call the manufacturer and technical support.


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A properly installed gas water heater complies with the codes and manufacturer's instructions. Correct installation will eliminate possible carbon monoxide poisoning and fires, flooding, electrical hazard, and other problems.

Every tank-type heater should be installed indoors in the vertical position, vent outside, and protected from freezing. The location of the installed gas water heater is particularly important if the tank or any element leaking. This is why an attic and the upper floors are not advisable. More about attic installation here.

The recommendation is to install a gas water heater in the location with the drainage, as close to the outside wall, vent terminal, and where it will provide easy access to operate and service the unit.

Avoid installing the heater directly on the carpet - use a metal or wood panel underneath the heater. Under every water heater, a suitable drain pan should be installed and piped to an adequate drain. Do not install the gas water heater in bedrooms, bathrooms, or other small and closed rooms where lack of air supply might affect clean and safe combustion.

Proper clearances from the combustible material should be given. Due to fire and explosion hazards, never store flammable materials close to the heater.

For mobile and manufactured homes, use a gas water heater designed for such applications or HUD-approved models.

TPR valve installation tips

It is crucial to have a listed temperature and pressure relief valve installed with a water heater (it should be factory provided) on. The TPR valve prevents any damage to the tank from the excessive temperature and pressure buildup. From the TPR valve, there should be a tube piped to within 6" of the drain, which should not be plugged or capped – no obstructions.

Installing the expansion tank

If the gas water heater is installed in the closed water systems, install the thermal expansion tank on the cold water supply to lower the temperature and pressure if they increase significantly inside the system.

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Installing a venting system

Make sure that there is enough fresh air inside the room where the heater is installed. If the gas hot water heater is installed in the confined space, two permanent openings should be provided at the specified distance from the floor and top of the enclosure.

The size of the opening depends on the total BTU of the unit. If the gas unit is installed in the unconfined (open) space, the air inside the room is enough for correct gas combustion.

Fresh air must be provided to the gas water heater so the flame can burn clean and with a blue glow. The air must enter the combustion chamber from below the unit and enter the flue vent below the draft hood - for the atmospheric vent models. Do not block the entrance, which often happens when using the insulation blanket. The exhaust vent has to be terminated outside of the building, made of the recommended material, and adequately sized.

A flue baffle has to be positioned in the flue tube, and vent connectors are correctly sized and securely fastened with screws. Avoid unnecessary bends, dips, or sags.

Other things to consider/include

A shut-off valve is a "must" in front of the unit so you can easily install the gas heater, troubleshoot and do the repairs.

A mixing valve is recommended to prevent scalding water, especially if kids are around. It connects hot and cold water, while the third pipe runs the diluted water (set to 120 F) to fixtures.

A gas pipe that connects the gas supply line and a gas valve should have a sediment trap (drip leg) with a 3" minimum length and manual gas shut-off valve.

Recommendations and tips

  • Read the rating plate found on the gas heater. Provided labels have useful information such as a guide for lighting the pilot light, type of gas, power, etc.
  • Install the manual gas shut-off valve so gas delivery to the heater can be stopped anytime in case of failure or emergency.
  • Install the drip leg.
  • Install a ground joint union between the shut-off valve and gas valve.
  • Test all connections for gas leaks with the soap-water solution.
  • Use dielectric unions or couplings when connecting a water heater to a copper pipe.
  • Shut off valve should be installed in the cold water inlet pipe.
  • Install the pressure reducing valve if water pressure is above the maximum allowed.

Notes for the safe gas water heater installation:

  • Never run a water heater if it is not filled with water.
  • Do not operate your gas water heater if flood-damaged.
  • Do not remove stickers and labels found on the outside surface of the water heater; there is some useful info there.

Always call a technician if in doubt or do not know how to deal with the problem.

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