How to Replace a Gas Water Heater like a Pro

Find everything you need to know about how to replace a gas water heater here.

Is your water heater leaking, has problems with the heavy sediment buildup, rust and noise, not producing enough hot water, or just not working?

Is it old and do you need a new one? When should I replace a water heater? Can I install a water heater myself? Who to contact for the replacement?

Rheem gas water heater (photo:

The answers to these and other similar questions are what you will find in this DIY guide, also learn how to replace a gas water heater in 10 easy steps.

See how long the gas water heater lasts, the reasons for the replacement, and when is the best time to install a new one. Learn how to deal with natural, propane gas, and plumbing work so you can save money and install a new unit properly and safely.

Replacing a water heater is the last thing you want to hear when having a problem with the hot water. Issues such as leaking, corrosion, element failure, and low performance are the main reasons for replacing the old and installing a new unit.

Like most of us, you will try first to fix the problem. If your gas heater is leaking, you will try to find where the leak is coming from and try to fix it. If the tank lining is corroded because of the aggressive hot water action, you can only replace a water heater.

If your gas water heater is not producing enough hot water, it may suffer from sediment buildup (due to hard water) and rust.

The recommendation is to drain and flush your gas appliance, but water heater replacement is what needs to be done if it doesn’t work. If you have a very old water heater, buying a new unit can be a good thing. New units are more energy efficient; they are equipped with the FVIR system, which protects the unit and the property from the accidental fire of the flammable vapors and is less prone to corrosion.

If you were happy with the performance of the old unit, hot water production, recovery rate, efficiency, try to match features when buying a new unit.

How to Replace a Gas Water Heater in 10 Easy Steps

Tools Needed for the Gas Water Heater Replacement

  • Pipe adjustable wrench
  • Tongue and groove pliers
  • Hacksaw or pipe cutter
  • Unions, fittings or flex connectors
  • Teflon tape or joint compound
  • Thin wire
  • Soldering torch
  • Wire brush
  • Appliance dolly to change the old with a new heater
  • Garden hose
  • Level
  • Screwdriver

I think this is the easiest and safest way to replace a water heater, a tank unit that uses propane/LP, or natural gas.

Important: Take precautions when working with gas; it is hazardous if gas starts to leak. For successful work, you need basic plumbing and gas skills and the right tools.

Step 1. Drain the Hot Water Tank

Your very first step in water heater replacement is to drain water from the tank. In short:

  • On the main water valve, turn OFF the water supply that supplies the home.
  • Turn the gas valve OFF.
  • Open the hot and cold faucets somewhere in the bathroom or kitchen above the unit (highest tap unit) and tap close to the unit (lowest point).
  • Take the garden hose and attach it to the water heater’s drain valve located at the bottom of the unit.
  • Open the drain valve and drain all the water from the tank.

A step-by-step guide on how to drain water from the gas tank-type water heater is described here.

Step 2. Remove the Flue Pipe

On the atmospheric-type gas water heaters, the vent pipe is made of sheet metal segments connected with the screws.

Separate the flue from the draft hood, and remove only those elements to free up some space for easy access. Mark the parts if needed so you know how to bring them back and in the proper order.

Clean the vents off if they are covered with dust and other residues but be careful not to bend or damage any part of the duct. Replace the flue pipe if it is corroded or if it has lost its functionality.

Power and direct venting are also easy to remove; the power vent type uses a plastic pipe attached to the heater’s exhaust adapter, while the direct type often uses a metal flexible pipe and adapter, which can also be easily disconnected. If you are not sure what is considered as proper venting and how to remove exhaust gases safely from home, check out this article.

Step 3. Disconnect the Gas Line

Close the gas valve on the main gas supply line and the gas control valve on the unit. To confirm that the gas line is disconnected properly, check the pilot light; it should be out.

If the gas unit uses a flexible gas line or copper pipe, use the adjustable wrench to disconnect it (unscrew the nut) from the gas control valve.

If the gas line uses rigid pipes (depending on local regulations), loosen the line unions using two wrenches. Disassemble the threaded “TEE” and “drip leg.”

You must be very cautious during the water heater replacement and when dealing with any gas work. Even small thread damage can produce gas leaking. If you accidentally damage the gas control valve – here is the guide on how to replace the valve.

Step 4. Disconnect the Plumbing Lines

Water lines are located at the top of the water heater. An incoming cold water pipe has a blue ring while the hot outgoing pipe has a red.

If your gas appliance uses rigid galvanized pipes, merely open the unions close to the unit using adjustable wrenches.

If using a solid copper pipe, cut the pipe just below the shutoff valve. Be sure to have the cut straight and take all the particles out. For a new installation, prepare the copper pipe for soldering by removing burrs, polishing, and applying the soldering paste.

Plastic CPVC pipes are also easy to use and remove.

The simplest way is if the unit uses flexible copper connectors as it is straightforward to disconnect it with a wrench. The use of such connectors depends on the local codes and the manufacturer’s recommendation.

Step 5. Remove the Old Unit

Once the flue pipe, gas, and water line are removed or disconnected from the water heater, proceed to the unit’s removal.

Make some room for the new gas heater by moving the old unit out. Keep in mind that the old heater can be heavy, especially if it has a problem with the sediment buildup, so use wisely all the help you need, a dolly cart, for example.

If you need help to choose the right gas heater, there is some excellent information (a guide actually) on how to select a heater, money-saving tips, reviews of different brands and manufacturers here, or if using the navigation bar with links to Rheem, AO Smith, and other manufacturers.

Bring the new unit in. If the size and features are the same, the odds are you don’t have to adapt the water line, gas line, or duct line.

At this point, you are half done with your water heater replacement; you just have to put everything back but in reverse order.

Step 6. Connect the Water Heater and Home Plumbing

First, check the local codes, manufacturer’s requirements, and recommendations on what type of water line you can install (CPVC, copper, or iron).

If the solid copper pipe is the best option, use it. Connect the home plumbing and water heater, combining the copper pipe and correct copper fitting and soldering.

If you have to work with the galvanized pipe, use a wrench and union to make a connection, but first, make sure to seal the threads.

The easiest way is using the flexible copper or stainless steel connector.

The temperature and pressure relief valve or short TPR valve, as the safety element, must be installed on the heater. Most of the time, it is built-in by the manufacturer but can also be provided disassembled.

Step 7. Connect the Water Heater and the Gas Line

Hook up the gas line using a rigid (iron) pipe, usually called a black pipe, or a flexible connection (check local code). Use the pipe joint compound or Teflon tape for all male-type threads. Take the gas “T” fitting with a capped nipple at the bottom and use a wrench to tighten it to the pipe and connect it to the gas valve on the heater.

The upper end of the nipple will be connected to the gas line and the bottom to the drip leg so that it can collect sediments, dirt, and moisture from either natural or propane gas.

Keep in mind that a licensed professional should do any work on the gas line and devices. You can contact a water heater expert here.

Step 8. Check the Gas Line for Leaks

Once done with the gas line, open the main gas valve and use soapy water and a brush. Apply soapy water on all connections, and if the bubbles appear, the gas is leaking.

The solution to this problem is easy; you have to tighten the connection. If gas is still leaking, turn off the gas valve, dismantle all the fittings, clean it carefully – especially treads, seal it, don’t over tighten, and rerun the test.

Step 9. Install the Flue Pipe

Reusing the old vent pipe makes sense as long as it isn’t damaged and you don’t have any problem with the performance of the previous heater. If the size of the unit is the same and if the flue pipe is not broken, has no cracks or rust elements, and there are no changes in bends and diameter, there is no need to get a new one.

Once the flue is cleaned from the dust, residues, sediments, and rust install it in the same order those marked segments and with the same inclination. Don’t forget to put screws back and connect the flue pipes.

Step 10. Light the Pilot Flame

This is the last step in the water heater replacement mini-guide. Excited?

It wasn’t that hard, right?

Turn the water valve ON and open the nearest hot water tap so the air is not trapped in the heater’s tank and water lines. When the water flows freely, close the tap – the air is gone.

Start the unit by lighting the pilot or activating the igniter on the gas control valve by switching to the ON position. You should be able to hear the ignition sound. The ignition procedure is usually described on a sticker.

Also, you can read an article on how to light a water heater and find the detailed instructions. Keep in mind that most manufacturers have a similar procedure for lighting/relighting the pilot light. Pilots are easy and safe to light and don’t require any special tools or a professional.

Video – How to Install a Gas Water Heaters (Lowe’s)


As it can be seen, gas water heater replacement isn’t complicated. These are the basics of how to remove the old and install a new water heater.

Keep in mind that the average lifespan of the tank-type gas water heater is 8-12 years, but the replacement can take place sooner if, for example, you want to install better performing and efficient unit or irreparable problems occur.

The cost for DIY replacement is a few hundred dollars, but it depends on the complexity. If you are not sure how to do it, do not have the right tools and skills, hire a plumber.

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