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

Gas Water Heater Installation

It comes to a time when a water heater replacement is essential, but it need not be overly expensive. 
Gas water heater installation may seem intimidating, but it's actually easier than you may think. 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, follow the instructions below for some guidance. 

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 (read our pick of the best tankless gas water heaters) 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 consider transitioning to a tankless water heater and take advantage of the fuel efficiency benefits (and money saving) they have to offer. 

Installing Your Gas Water Heater

Before getting started, there's a few things you'll need to get your gas water heater installed correctly. The following is a list of tools and supplies you'll need:

Step 1 - Remove the Old Water Heater

Gas Water Heater Installation - Turn off the gas
  • Turn the gas supply off to the water heater.

Gas Water Heater Installation - Remove the gas line
  • Use a wrench to disconnect the gas line to the old water heater.

Disconnect the venting
  • Inspect and detach the venting to the water heater.
  • Set the venting aside. You'll use it later.

Turn off water
  • Open a hot water faucet in your home, and let the water flow until it is cool.
  • Shut off the incoming water supply to the water heater.

Drain the tank
  • 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.

Remove the T&P Discharge Pipe
  • Remove the T&P discharge pipe from the T&P valve.
  • Set the discharge pipe aside. You'll use it later.

Remove the water lines
  • Disconnect the water supply pipes.
  • Remove the old water heater using a hand truck.

Step 2 - Install the New Water Heater

Install the Discharge Pipe
  • Place the new water heater in a drain pan.
  • Install the discharge pipe to the T&P relief valve.

Line Nipples
  • Apply plumbers tape (white) to the hot and cold heat trap nipple threads.

Attach the Water Lines
  • Attach the flexible hoses to the hot and cold water nipples.
  • Use the dielectric fittings if required in your area.

Line connector
  • Use plumbers tape (white) to line each end of the connector body.

Secure connector body to hose
  • Secure the flexible hose to one end of the connector body.

Connect the top of the water line
  • Hold the other end of the hose up to the pipe and use a pencil to mark where to cut. Be sure to leave a little slack in the hose.

Cut the pipe
  • Cut the pipe and remove the burs.

Connect pipe using compression nut
  • Slide the compression nut onto the pipe.
  • Push the pipe into the fitting and tighten the compression nut. 

Install Earthquake Straps
  • Install earthquake straps to secure the water heater to the wall.

Step 3 - Fill the Water Heater Tank

Turn on Water
  • 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.
  • If there are no leaks, fill the tank full of water.
  • You'll know the tank is full when the water runs from the open faucet.
  • Close the open faucet once the water stops sputtering.

Step 4 - Attach the Venting and Gas Line

Attach the venting
  • Connect the venting to the water heater.

Secure the venting to the hood
  • Attach the venting to the exhaust hood using self-tapping sheet metal screws.

Set the control knob to off
  • Set the control knob to OFF on the water heater's control valve.

Wrap the fitting with gas plumbers tape
  • Wrap the fitting threads with gas plumbers tape (yellow).

Insert the flare nut into the control valve
  • Insert the flare nut into the control valve.

Attach the flare nut into the gas line
  • Screw the other flare nut onto the gas line.

Connect the gas line to the flare nuts
  • Connect the flexible gas hose (yellow) to each flare nut.

Gas Water Heater Installation - Turn off the gas
  • Turn the gas supply ON.

Check the fittings with leak detection solution
  • Use leak detection solution on the gas fittings. The solution will bubble if there's a leak.
  • Tighten connections as needed.

Install the air filter
  • Follow your manufacturers guidelines on how to light the pilot.
  • Check that your water heater is properly venting.
  • Install the air filter.

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