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

Find out how to install a gas water heater with our step-by-step guide and easy-to-follow instructions. Learn about the best location for the large cylinder, venting, and plumbing requirements, as well as the tools you’ll need and how to avoid common problems.

It’s important to follow state and local codes and the manufacturer’s instructions when installing a gas water heater to ensure reliable and safe operation. For example, one requirement may be to install an expansion tank on the incoming water supply line in a closed heating system. Some codes may also require a special license to connect the gas line to your heater, comply with venting regulations, and install a vacuum relief valve, among other things.

Can I Install a Gas Water Heater Myself?

Yes, you can install a gas heater yourself, but only if you know how. For your reference, detailed instructions are below.

This is not an easy DIY job and can be very costly and dangerous if not done correctly. For proper installation and worry-free operation, you need to have more than basic knowledge and experience to safely handle any electrical, plumbing, and gas work.

In addition, you might need to get the permits from your local building department.

Gas Water Heater Installation: Required Tools

Whether you want to replace an old or install a new gas water heater, most of the required tools are found in almost any handyman home, and these include:

• Adjustable plumbing wrenches
• Power drill
• Pipe cutter
• Screwdriver
• Garden hose for draining
• Plumbing sealant or tape
• Also: pipes, fittings, valves

Where to Install a Gas Water Heater?

Before installing a gas water heater, you should carefully select an indoor location as its placement is crucial for the safety of the occupants, economical and efficient use of a unit. Keep in mind that the tank-type models, as opposed to tankless, can only be installed indoors.

Your device should not be installed in the area where gas or water leakage from the heating system can damage adjacent areas and lower floors and cause damage to the structure.

The risk of the water and gas leak, difficulties in maintaining, service, handle, removal and control, are the reasons why some plumbers do not recommend attic installation, even knowing that some homes (especially those with the slab foundation) already have it installed.

To ensure the proper water and gas flow, the floor where the unit will be standing must be on a level surface. Specific local codes might require a stand to raise a heater and provide a required clearance.

That is why it is essential to provide the correct drainage solution under the heater, like a drain line or drain pans. Since the burner and air inlet are located in the lower part of the tank, your drainage solution must not restrict this entrance.

The selected location must provide adequate clearance for servicing and maintenance. Do not put the tank directly on the carpet, but slide the piece of metal or wood panel beneath if you have to.

During the installation, keep in mind that combustible and flammable products, like paint, propane, gasoline, should never be stored in the same room or close to the unit. Most modern devices are equipped with the FVIR system, which ensures that there will be no ignition of the flammable vapors outside the combustion chamber.

To reduce the energy waste and if the water line is too long, insulate the pipes to protect them from exposure to freezing temperatures. You can always wrap the heater with an insulated jacket or blanket and reduce the standby loss. Before you install the unit, make sure, if possible, to place it close to the most used application and a power source.

Install your tank-type gas unit only in the designated room, not in the bathroom, bedrooms, or any unprotected outdoor location. You want to place your unit close to the external wall to make room for the vent pipes. This is why garages, laundry rooms, and basements are good spots.

Related: How to light a gas water heater (with the pilot light)

Venting Requirements

Install a gas water heater close to the external wall to ensure an unobstructed venting, short vent pipe run, and sufficient fresh air for the normal operation.

When installing your heater in the confined space, two openings have to be made for adequate combustion and ventilation air intake. One opening is located 12″ above the floor and the other 12″ from the ceiling. The total free area of the opening depends on the heater’s BTU.

Check also if the vent connectors are properly secured, flue baffle installed in the flue tube, connected to the chimney or vent pipe system, and at a safe distance from other combustible materials. Also, make sure they are supported with the metal hanger and at the specified distance. Do not operate the unit if the flue baffle is not installed. The manufacturer’s instructions must be followed.

Note: The building code dictates venting requirements, either dealing with the power vented, direct vent or atmospheric models. It is required to install a unit per code, and with the potential problem that might arise, it is recommended to contact a professional technician.

If the vent kit is supplied with the unit, it must be installed per the manufacturer’s instructions, such as following the minimum rise, termination setup, sealing the vent kit joints, proper clearances, and others.

Things to Know When Installing an Atmospheric Type Water Heater

The vent pipes of the atmospheric type water heaters must provide an upward, natural movement of the hot air. The flue gases moved by the natural draft are directed from the combustion chamber through the draft diverter, metal vent pipe, chimney, and outdoors. If the house does not have a chimney or similar, using this type of heater can be expensive to install.

Proper venting depends on the pressure difference between the highest and lowest point on the vents, including the surrounding air pressure. Any obstruction leads to back drafting, gas spillage and exposure to carbon monoxide.

For the natural draft type models, it is recommended to use a galvanized steel pipe or preferably B-vent (double-wall vent pipe) secured to the draft hood with sheet metal screws. The size is usually 3″ or 4″, depending on the unit capacity.

The problem with the single wall vent pipe is that it might cause excessive condensation if used in colder areas (a garage, for example).

For the proper draft, the metal pipe between the heater and chimney must run upwards, rising not less than 0.25″ per foot, and should be straight and as short as possible.

The surrounding air, which enters the house from the outside, is used for gas combustion and dilution. If the house is tightly sealed, this can lead to a problem as there will be no sufficient air coming in – other venting options should be considered.

Useful Tips When Installing a Power-Vented Water Heater

As opposed to atmospheric type water heaters, power-vented (PV) models, also known as an induced draft or fan-assisted, can have the venting pipes installed either horizontally through the sidewall or vertically through the roof.

This is because PV models use the electric blower (fan) and dedicated vent pipes, usually made of PVC. The blower, mounted on top of the unit, guarantees proper venting and eliminates the risk of negative pressure buildup inside the home.

PV models are often found on energy-efficient models and are recommended for homes without a chimney or where it is hard to install the atmospheric type. However, they are more expensive.

What You Need to Know When Installing a Direct-Vented Water Heater

Direct vent water heaters (DV) also rely on the natural draft for proper venting. This type is excellent for homes with no chimney and no electric source located close to the unit. The advantage is that you will have hot water even if the power goes out.

DV models are designed with a single or dual vent pipe system. Single-vent models use the surrounding air for combustion and one vent pipe to move the exhaust gases outside the building.

Dual-vent models utilize two pipes, where one pipe is used to draw the fresh air from the outside, while the other pipe is used as an exhaust.

As the air is coming from the outdoor, DV models, do not have a problem with insufficient indoor ventilation.

How to Check for Proper Venting

Use this test to check if the venting on your gas water heater is proper:

• Make sure all the windows and doors are closed and the unit is running.
• Take the extinguished match and put it near the vent hood.
• If the venting system is operating correctly, the smoke from the match should pull into the vent hood. If it blows back, there is a problem. This issue must be fixed as soon as possible as there is a risk of carbon monoxide poisoning.

How to Install a Gas Water Heater in 15 Steps

1. Turn the unit off. Turn the power off on the electrical panel. Shut off the gas supply on the gas control valve and water supply on the shut-off valve.
2. Remove the water from the tank. Attach the garden hose to a drain valve to empty the tank. See details on how to drain a water heater fast and easy.
3. Remove the vent pipe when replacing the old model.
4. Disconnect the gas line. Use the adjustable wrench to unscrew the pipe at the union fitting, but keep the T fitting and sediment trap.
5. Disconnect the water lines. Using the same adjustable wrench, disconnect both cold and hot water lines from the top of the unit. Or, cut the copper lines if soldered.
6. Remove the TPR discharge pipe.
7. Remove your old water heater and dispose it of properly.
8. Prepare the site for a new unit.
9. Position a device in an adequate location with the drain pan underneath to collect any leaks.
10. Install heat traps on the device and connect both hot and cold water lines to these fittings. We recommend using flexible braided stainless steel lines for easy installation and service. To prevent corrosion of the fittings use dielectric unions when connected to copper pipes.
11. Install a new temperature and pressure relief valve and the overflow pipe.
12. Connect the gas line. You can connect the piping to the gas control valve either by using the flexible connector or black iron pipe. Make sure everything is clean and sealed. And remember, always check for leaks.
13. Turn the gas, electrical, and water supply on. 
14. When filling the tank with water, the drain valve must be closed. And when the heater is in use, the cold water supply must be left open. Open the nearest hot water faucet to let the air exit and ensure constant flow.
15. Light the pilot (if available), or start the unit per instructions.

The tank can be filled only when the gas and water supply are connected – preferably by a licensed plumber. When the air is removed from the heating system, the gas supply can be activated and tested for leaks. Never use a hot water heater unless it is full of water.

Installation Tips When Connecting a Gas Line

• Check if the gas type and pressure supplied to the heater are the same as indicated on the rating plate. If not, contact the supplier.
• A manual shutoff valve must be installed in the gas supply line and close to the unit.
• The gas regulator control valve has a 1/2″ female threaded connection, which is typical for most gas models.
• After you are done with the gas water heater installation, always check connections for the leak. Use a solution of dish-washing soap and water and apply to the gas pipe connections. A leak will cause the soap to bubble. If there is a leak, tighten the loose connection, and check again.
• Per building codes, a drip leg or sediment trap should be installed to collect any small particles or moisture present in the pipeline.
• A union must be installed between the gas control valve and shutoff valve, for easy maintenance.

Connecting piping to the heater’s control valve can be accomplished by either a flexible connector or black iron pipe.

Installation Tips When Connecting Plumbing

Plumbing work includes connecting your home plumbing and the cold water inlet and hot water outlet (3/4″ NPT male thread), including the following elements:

• Dip tube installed in the cold water inlet
• Shutoff valve
• Union installation so the heater can be easily disconnected if needed
• Temperature and pressure relief valve installation, including the discharge line
• Check valve and pressure reducing valve, if needed
• Expansion tank

The following instructions are based on the assumption that an old water heater has to be replaced.

If your home plumbing uses the galvanized pipes, remove the pipe close to the heater and at the nearest fitting.

If it uses copper or plastic pipes, simply cut the pipe close to the unit using the pipe cutter.

To make a connection between the water heater and plumbing, you have several options; hard or flexible connections. Flexible is better, especially when the existing pipes do not line up with the new heater connections. And it is faster to put it on. But first, check the codes.

To make the hard connections, you will need more than basic skills and the right fittings to line up the pipes, while with the copper pipes, there will be some cutting and soldering.

With the plastic pipes, it is even easier, using the right fittings and sealants where needed. Just keep the plastic pipes at least 6 inches away from the hot surfaces.

How Much Does It Cost to Install a Gas Water Heater?

According to homedepot.com, the average gas water heater installation cost is between $1300 and $2000, including a basic model, permits, material, labor, and removal of the unit.

As per homeadvisor.com, you will pay between $45 and $150 an hour just to hire a plumber and between $831 and $1651 to purchase a storage tank heater and have it installed by the plumber.

Also, as per homeguide.com, an average labor cost for the gas water heater installation is between $200 and $1000, which is cheaper than if done through the Home Depot or Lowe’s ($400-$1100).

And for your reference, it usually takes from 2 to 6 hours to install one.

Final Notes

When it comes to installing a gas water heater, safety should always be your top priority. While the information we’ve provided here can be a helpful reference guide, it’s essential to seek the assistance of a licensed installer or plumber to ensure that the installation is compliant with legal codes, regulations, and manufacturer’s instructions.

Attempting to install a gas water heater on your own can be dangerous, as it requires specialized knowledge, tools, and skills. By working with a professional, you can be confident that your new water heater will be installed correctly and safely, without the risk of leaks, fires, or other hazards.