How to Install a Gas Water Heater

A general rule is that if you have water on the floor or on top of the unit (different from water leaking from a supply line above the unit), you’ll probably need to change your hot water heater. The data plate on your current tank has size and energy specifications that help make buying a comparable unit easier when thinking about how to change a gas water heater. It should also have the date of manufacture. Most gas water heaters typically last between 8 to 15 years. If your family has grown larger or smaller, this is a good time to consider upsizing or downsizing your water heater.

The expansion tank connects onto the cold-water supply line near/above your water heater. You can install an expansion tank using push-fit fittings. They slide onto the pipe, no soldering needed. If you decide to solder, de-burr and clean pipes and fittings. Apply soldering paste and assemble. Heat the fitting and solder.

A water heater expansion tank prevents hot water from backflowing into the cold water line It also guards against hot water from escaping through the pressure relief valve and onto the floor. Proper installation of a thermal expansion tank can solve all these issues. 

The expansion tank pressure must match the main water pressure to work effectively. Refer to the manufacturer’s installation instructions for the correct method to balance the water pressure.

Open a faucet on hot and let it run until the water runs cool. Then, shut off the water supply. Connect a garden hose to the drain valve at the bottom of the tank. Open the valve and let the water empty into a bucket, down a drain or let it drain outside.

When the tank is empty, remove the discharge pipe from the T&P (temperature & pressure) relief valve. You may reuse the discharge pipe, but do NOT reuse the old T&P relief valve.

Disconnect the water supply pipes. If you have to cut them, leave them as long as possible. Have someone help you remove the old water heater.

Install the discharge pipe from the T&P relief valve toward the floor. If there is no drain underneath the pipe, put a bucket underneath to catch water dripping from the discharge pipe. Cut the pipe so it is no more than 6 inches above the bucket.

Use a flexible hose kit with flexible water hoses and a gas hose for utility hook-up. Apply plumbers tape to the threads of the heat trap nipples where you’ll connect the water hoses. Then, attach the water hoses. You’ll use the gas hose in a later step.

Some areas require dielectric fittings to reduce corrosion between two different metals. Your area’s local codes and ordinances should detail the specifics of installation in your area.

Apply plumber’s tape to the connector body threads. Secure the fitting to the hose, and then hold the hose up to the pipe. It should have a little slack. Mark and cut the pipe, removing any burrs.

Slide the compression nut and ring onto the pipe. Push the pipe into the fitting and tighten the nut.

To fill the tank, remove the aerator from the nearest faucet and open the hot side. Slowly turn on the main water supply and check connections along the water heater for leaks. If you are leak-free, fill the tank. If you have leaks, shut off the water supply and gently tighten the connections. Repeat until the connections are secure.

Secure the new exhaust hood to the venting with screws.

Turn the tank’s gas control knob to the “off” position. Wrap the threads of your kit’s fittings with gas plumber’s tape (yellow).

Insert a flare nut into the control valve. Screw the other flare nut into the gas line. Connect the hose and tighten.

With the control knob set to “pilot,” press the knob and push the igniter button. The light will blink when it’s lit and you should see a small flame through the view pane. Set the temperature to 120 degrees Fahrenheit. Always refer to your owner’s manual on how to start a gas water heater.

Install the air filter.

After a few hours, check the discharge pipe that runs out of the T&P relief valve. A dripping pipe usually means the pressure is too high. Turn the pressure down below 80 PSI.

If a faucet stops running after installation, remove the aerator from the faucet in question and let the water run for a few minutes to clear loose sediment. Rinse and replace the aerator.