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How to Install a Gas Water Heater – Step by Step Guide

Fact checked by Stephen Conklin

how to install a gas water heater

Is your water heater leaking from almost every square inch that the only recourse you have is to replace it? Is your water heater nearing the end of its service lifespan? Replacing a water heater is a cinch if you know how to install a gas water heater.

Water heaters last only 15 to 20 years with proper care. Unfortunately, not all of us have the same domestic water characteristics impacting our water heaters. Some may only last up to ten years before requiring a gas water heater replacement.

Installing a new gas water heater to replace your old unit is easy if you follow the steps I will share.

Table of Contents

Things You Need for This Tutorial


You need to prepare the following things to remove and replace a gas water heater.

New Gas Water Heater

I recommend buying a gas water heater with a complete installation package. It would be best to check the fittings for compatibility with your existing setup. Otherwise, you will have to buy these materials.

Read the new gas water heater’s installation instructions because manufacturers may have different recommendations.


You need two pipe wrenches to work with gas and water lines. Other tools you might need include a screwdriver, soldering torch, pipe cutter, voltage tester, Teflon tape, tape measure, electrical tape, drills with bits, and safety glasses.


A discharge pipe is a must when installing a gas water heater, as are the fittings, pressure relief valve, pipe thread compound, and solder. You will also need gas and water tubing, a bucket, a dishwashing solution, an exhaust vent, and connectors.

Steps for Installing a Gas Water Heater


Step 1. Close the water and gas supply lines.

Replacing a gas water heater starts with removing the old unit. Unfortunately, it is unsafe to perform this procedure without closing the gas and water supply valves.

Check the water line supplying water to the water heater for any shutoff valve and close it. If you do not see any, you might want to shut off the valve at the main water supply line in your basement or front of the house.

Follow the gas supply line running from the water heater tank and check for a valve. Turn the knob about a quarter turn until it forms a right angle with the gas pipe.

Step 2. Empty the water in the water heater tank; loosen the gas line & pipe.

Locate your water heater’s drain valve. Connect a garden hose to the water heater drain valve and empty its content. Be careful when draining the water because it may be hot.

While draining the water, use two adjustable wrenches to loosen the union at the gas line opposite the gas control valve. Additionally, remove the pipe leading to the gas control valve using a pipe wrench.

Step 3. Cut the existing water supply lines and remove the old gas water heater tank.

Before cutting the cold and hot water lines to and from the water heater, you might want to loosen the vent pipe first.

Use a portable pipe cutter to cut the cold and hot water lines. Slide the old water heater tank out of the way and get ready with the new gas water heater installation.

Step 4. Install the temperature and pressure (T&P) relief valve into the new gas water heater tank.

Most gas water heaters already have the temperature and pressure (T&P) relief valve factory installed. If yours does not, you must secure this component into the tank’s port by twisting it clockwise to tighten. In this case, I recommend you learn more about how to adjust and the appropriate temperature of the water heater.

Wrap Teflon tape around the T&P relief valve threads before installation. Tighten it with a pipe wrench. Connect a discharge pipe to the T&P relief valve and position a bucket under the valve to catch any drips.

Step 5. Secure the water heater tank piping assemblies.

Cut 6-inch long copper pipes and solder these to 3/4-inch copper tube adapters. Secure the piping assemblies to the water heater’s cold water inlet and hot water outlet ports.

Experts recommend using plastic-lined nipples in the connections to protect them against corrosion. Slide the compression ring and nut over the water pipe to prepare the water heater connections.

Step 6. Mount the new water heater tank and connect the water supply lines.

Position the new water heater, ensuring the proper alignment between the water supply lines and the inlet and outlet ports.

You might also want to check your local building code to see if it requires seismic straps. This component stabilizes the water heater during earthquakes, ensuring you have a safe and secure hot water tank installation.

Slide the compression nut to meet the water pipes from the water heater. Secure the nuts with a pipe wrench.

Pro Tip: If the pipes do not align, you may want to install 45-degree elbow joints to offset the water supply lines.

Step 7. Reattach the exhaust vent to the gas water heater tank.

Reposition the exhaust vent over the water heater’s draft hood and secure it by tightening the screws. If the draft hood does not have holes, you must drill through it to fix the vent to the tank.

Ensure the exhaust vent has its first elbow at least a foot above the water heater tank.

Step 8. Connect the gas line to the new water heater tank.

Get a short gas pipe and apply a pipe joint compound on the threaded ends. Screw one end of the tube into the gas control valve and tighten it to secure it.

Remember how the gas line connects to the old water heater’s gas control valve? You will have to recreate the connections by using new nipples. Finish this step by securing the gas water pipe union.

Step 9. Fill the tank with water.

Remove a faucet’s aerator to relieve pressure in the system. Open a hot water tap. Next, open the main water supply shutoff valve.

Check the water heater joints for leaks. If you notice leaks anywhere along the water supply line, close the shutoff valve and retighten the connections.

If there are no leaks, leave the faucet open and let the water flow.

Step 10. Assess the newly installed water heater for back-drafting.

A gas hot water heater installation is never complete without assessing the presence of a backdraft.

Close windows and doors before turning on the bathroom and kitchen exhaust fans. Open a hot water tap near the water heater and leave the water running. Listen for gas burner ignition from the heater.

Light a match and put out the fire, leaving only smoke. Position the smoking matchstick near the draft hood. You should see the smoke go up the exhaust vent. If it does not, close the gas supply line and call an HVAC professional.

Step 11. Check for gas leaks.

Installing a gas water heater is risky with improper gas connections. That is why you must always check for gas leaks before wrapping up the installation.

Make a dishwashing & water solution and apply it over the gas connections. If you see bubbles, you have a gas leak. If you are unsure, I recommend using a gas leak detector.

Step 12. Activate the gas water heater pilot light.

Follow your manufacturer’s instructions on how to light the gas water heater’s pilot light.

Most water heaters only require pressing and holding a pilot control button and clicking the igniter button after turning on the pilot knob. Other models need a barbecue lighter to ignite the pilot light, while others have electronic ignition.

Here is a gas water heater installation video from Lowe’s Home Improvement you might want to see.


Learning how to install a gas water heater seems intimidating to some people. However, following the steps I outlined in this guide will help you feel more confident about replacing your old water heater. Your family will love the effort you put into this activity.

Did this guide strengthen your confidence in installing a gas water heater? If yes, would you share this tutorial with other people as well? If you have comments or questions, know that I am willing to listen and share my thoughts, too.

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