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How to Install a Gas Water Heater

Install a new gas water heater to save money on your utility bills. Our video and step-by-step guide shows you how.

Before You Begin

Determine the cause or need for a new water heater with a quick maintenance assessment before embarking on a full replacement.

If you follow the steps below and determine that replacement is necessary, check local building codes before you get started to ensure compliance. And, if you’re not comfortable, call a pro.


Step 1

Checking old venting with a match.

Gas water heaters need proper venting for operation. To check the venting on your existing unit, close all windows and doors and turn on all gas appliances and exhaust fans and turn up the temperature on your water heater for a few minutes. Then, hold an extinguished match near the vent hood. The smoke should pull into the hood. If it blows back at you, you have a venting problem. Call a professional for help. If you do end up installing a new water heater, you will repeat this test with the new unit.

Step 2

Data label on the side of a gas water heater.

A general rule of thumb is that if you have water on the floor or on top of the unit (this is different from water leaking from a supply line above the unit), you’ll probably need a new water heater. The data plate on your current tank has size and energy specifications that help make buying a comparable unit easier. If your family has grown larger or smaller, this is a good time to consider upsizing or downsizing your water heater.

Check Water Pressure

Your home’s water pressure is important for all water-using appliances. Reduced pressure lessens stress on plumbing lines and extends the life of appliances and fixtures. You might want to consider an inline pressure gauge for pressure monitoring.

Step 1

Pressure gauge attached to outdoor hose to check home's water pressure.

Check your home’s water pressure using a pressure gauge on your outdoor spigot; 50-60 PSI is ideal. If your home’s water pressure is greater than 80 PSI, lower it with the pressure-reducing valve installed after the main water shut-off. If your home doesn’t have a pressure-reducing valve, a professional can install one for you.

Add an Expansion Tank

Layout of hot water heater components along the water line.

Step 1

Expansion tank on water line.

Determine which expansion tank you will need. A thermal expansion tank alleviates excess pressure in the lines of a closed system. A 2-gallon expansion tank works with water heaters up to 50 gallons. A 5-gallon expansion tank is needed for water heaters up to 100 gallons. Check the manufacturer’s recommendations for exact sizing.

Step 2

Push-fit fittings on the expansion tank.

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.

Step 3

Pressure relief tank.

The expansion tank pressure must match the main water pressure to work effectively. Use a hand air pump to increase pressure or depress the valve to lower it.


Use only piping, sealants and solder suitable for potable water when working with water-using appliances.

Removing the Old Gas Water Heater

Step 1

Disconnect gas pipe from the control valve.

Turn off the gas and use a wrench to disconnect the gas pipe from the control valve.

Step 2

Detach the exhaust hood and initial stretch of venting. Leave the rest in place. If the existing venting is rusted or in disrepair, this is a good time to replace it.

Step 3

Drain water heater tank into buckets or down a drain.

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 or down a drain.

Good to Know

Opening a hot water faucet may help the water drain faster.

Step 4

Removing the discharge pipe from the T&P valve.

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.

Step 5

Remove water supply lines.

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.

Installing the New Gas Water Heater


Exercise caution when unloading and unwrapping your new water heater. Water heaters are heavy; use a helper, an appliance dolly and/or a hand truck when moving the appliance.

Step 1

Gas water heater sitting in drain pan.

Place the new water heater in a drain pan (on or off of the pedestal as determined by your local building codes). You can avoid possible flooding by routing pipe to a drain from the drain pan.

Step 2

If your water heater did not come with a new T&P relief valve pre-installed, simply twist in the new valve now. It may be in the box or you may need to buy your own. Do NOT reuse the old valve. The T&P valve automatically opens if the temperature or pressure becomes too high for the tank.

Step 3

Discharge pipe over bucket.

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.


Only use copper or CPVC pipe for T&P discharge.

Step 4

Plumbers tape around threads.

Use a flexible hose kit with a gas hose for utility hook-up. Apply plumber’s tape to the threads of the heat trap nipples. Then, attach the hoses.

Step 5

Dielectric fittings.

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.

Step 6

Threads of the fitting wrapped.

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.

Step 7

Compression nut in place on pipe.

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

Step 8

Illustration of seismic straps to hold a gas water heater in place.

Some areas require seismic straps to prevent earthquake damage. These straps brace the water tank against the wall to keep the unit from toppling over. If you’re not in an earthquake zone, skip ahead to the next step.

Seismic straps should be installed approximately 6 inches from the top of the water heater and 18 inches from the bottom. Locate the wall studs closest to the strap measurement and drill pilot holes.

Secure one end of the strap to the stud with a socket and ratchet. If block covers the studs, use a masonry bit to create a pilot hole. Wrap the strap around the water heater and adjust the size, securing the adjustable bracket on the opposite side.  Pull the strap tight and repeat the process on the lower strap.


Defer to the manufacturer’s instructions for seismic strap installation.

Step 9

Touch test to check water supply lines for leaks.

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.

Step 10

When water runs from the faucet, the tank is full. Let the water run for three minutes to empty air and debris out of the tank.

Step 11

Exhaust hood on new water heater.

Secure the new exhaust hood to the venting with screws.

Step 12

Gas tape on fittings.

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).

Step 13

Complete gas hook-up for a gas water heater.

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


Make sure your home is properly equipped with carbon monoxide detectors if you have gas appliances.

Step 14

Control knob set to pilot.

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.

Good to Know

Read your manufacturer’s lighting instructions for more detailed instructions on lighting the pilot.

Step 15

Perform the vent test again. If smoke blows back at you, call a professional for assistance.

Step 16

Air filter installed around bottom of gas water heater.

Install the air filter.

Step 17

Reducing pressure at valve.

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.


Water from the discharge pipe may be hot.

Step 18

Removing the aerator to clear clogged lines.

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.

Preventing Scalds

Even with the temperature gauge set to 120 degrees, scalds are still a concern. Children, older people and those with sensitive skin are especially at risk. To prevent injury, consider installing thermostatic mixing valves.

Installed at the point-of-use faucet, fixture or appliance, a thermostatic mixing valve controls both the volume and temperature of water by attaching to both the hot and cold water supply. The settings may be adjusted inside the valve itself to provide optimum comfort.

Step 1

Turn the water supply off and use only materials (tape, pipe, solder, etc.) that are safe for potable water (because the water may be ingested).

Step 2

Solder the connections to the valve before attaching to the plumbing. Connect the valve to the hot and cold water supply and the outlet pipe. If additional soldering is needed, maintain a safe distance from the valve because excessive heat may cause damage.

Step 3

Turn the water supply on to test for leaks. Tighten and correct as necessary. Follow the manufacturer’s instructions for adjusting water temperature.


Defer to the manufacturer’s instructions for installing a thermostatic mixing valve.