How to Install a Gas Water Heater: A Step-by-Step DIY Guide

Gas Water Heater Installation

Gas water heater installation may seem intimidating, but it's actually easier than you may think, although, if the job is bigger than you want to tackle you can always hire a professional plumber. They'll be happy to install your gas water heater and dispose of your old unit as well. But if you're up for the challenge, you can save yourself some money by doing it yourself.

The average service life of water heaters is 8 to 12 years, so if yours is entering old age, you may want to consider purchasing a new unit versus repairing your old water heater.​ Keep in mind that in most situations it's generally best not to switch fuel types (gas or electric), although sometimes it does make sense. You may also want to transition to a tankless water heater and take advantage of the fuel efficiency benefits they have to offer. 

Installing Your Gas Water Heater

Necessary Supplies


Step 1 - Remove the Old Water Heater

  • Turn off the gas to the water heater. 
Gas Water Heater Installation - Turn off the gas
  • Use a wrench to disconnect the gas line to the old water heater.
Gas Water Heater Installation - Remove the gas line
  • Inspect and detach the venting to the water heater. 
  • Set it aside to be used later. 
Disconnect the venting
  • Open a hot water faucet in your home and let it run until the water is cool.
  • Shut off the incoming water supply to the water heater.
Turn off water
  • Connect a garden hose to the drain valve. 
  • Open the drain valve and drain the tank.
  • The water may contain sediment. If you have difficulty draining the tank, check out this article to help you unclog your drain valve.
  • Open a hot water faucet to allow air to enter the tank.
Drain the tank
  • Remove the T&P discharge pipe from the T&P valve.
  • Set the discharge pipe aside to use later.
Remove the T&P Discharge Pipe
  • Disconnect the water supply pipes.
Remove the water lines
  • Remove the old water heater with a hand truck. 

Step 2 - Install the New Water Heater

  • Place the new water heater in a drain pan.
  • Install the discharge pipe to the T&P relief valve. 
Install the Discharge Pipe
  • Apply plumbers tape to the hot and cold heat trap nipple threads.
Line Nipples
  • Attach the flexible hoses to the hot and cold water nipples.
  • Use the dielectric fittings if required in your area.
Attach the Water Lines
  • Use plumbers tape to line each end of the connector body. 
Line connector
  • Secure the flexible hose to one end of the connector body.
Secure connector body to hose
  • Hold the other end of the hose up to the pipe and mark where to cut. Be sure to leave a little slack. 
Connect the top of the water line
  • Cut the pipe and remove the burs. 
Cut the pipe
  • Slide the compression nut onto the pipe.
  • Push the pipe into the fitting and tighten the compression nut. 
Connect pipe using compression nut
  • Install earthquake straps to secure the water heater to the wall. 
Install Earthquake Straps

Step 3 - Fill the Water Heater Tank

  • At the nearest faucet, remove the aerator and open the hot water side.
  • Turn on the cold water supply to the water heater and check the fittings for leaks. 
Turn on Water
  • If there are no leaks, fill the tank full of water.
  • The tank is full when the water runs from the open faucet. 
  • Shut off the open faucet once the water stops sputtering. 

Step 4 - Attach the Venting and Gas Line

  • Connect the venting to the water heater.
Attach the venting
  • Attach the venting to the exhaust hood using self tapping sheet metal screws​.
Secure the venting to the hood
  • Set the control knob to off on the water heaters control valve.
Set the control knob to off
  • Wrap the threads of the fittings with gas plumbers tape (yellow).
Wrap the fitting with gas plumbers tape
  • Insert the flare nut into the control valve.
Insert the flare nut into the control valve
  • Screw the other flare nut onto the gas line.
Attach the flare nut into the gas line
  • Connect the flexible gas hose (yellow) to each flare nut. 
Connect the gas line to the flare nuts
  • Turn the gas supply on.
Gas Water Heater Installation - Turn off the gas
  • Use leak detection solution on the gas fittings. It will bubble if there is a leak.
  • Tighten connections as needed.
Check the fittings with leak detection solution
  • Follow your manufacturers guidelines on how to light the pilot. 
  • Check that your water heater is properly venting.
  • Install the air filter.
Install the air filter

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