Because professional installation often adds $500 or more to the cost of replacing a standard tank-style water heater, many homeowners naturally look to the possibility of installing it themselves. And while it is regarded as an advanced project, DIYers with good experience can often do the work themselves with a little planning. But this is not a project for beginners.
The first step to learning how to install a new water heater is to examine the type of heater you already have. First determine the fuel source: gas or electric? Then, determine the size: 30-, 40-, 50-gallon, or larger? When replacing a water heater, it's easiest to keep the same fuel type and roughly the same tank size. However, if your old water heater did not provide enough hot water, you can consider going with a larger unit—changing from a 40-gallon to a 50-gallon unit, for example—provided there is enough space for the larger heater.
In the best-case scenario, replacement is a matter of a few hours work disconnecting and removing the old heater, then moving the new one into place and restoring the connections in exactly the same fashion. There is a reason, though, why plumbers bid the job on the basis of a full day of work: it often becomes more complicated.
Replacing a water heater will require you to make both plumbing connections as well as wiring or gas hookups, plus a vent connection if you have a gas heater. If you're not confident of your skills in these areas, calling a pro is the best approach. In some areas, it may be illegal for homeowners to handle gas hookups. Always follow local ordinances when it comes to working with gas lines.
Gas Water Heater Venting
For many years, the standard means of venting combustion exhaust gases for a gas-burning water heater was with atmospheric venting. In this system, a metal draft hood at the top of the water heater channeled both exhaust gases and a small amount of fresh air from the room up a metal flue through the roof or to a common chimney. In many cases, installing a new water heater will be a matter of simply connecting the existing flue and draft hood to the new heater.
But the building code in some communities may require changing to a different means of venting whenever a new water heater is installed. Many areas now require a system known as direct venting, in which a special double-chambered vent pipe carries the exhaust gases out the side of the house at the same time fresh air is allowed in. This is often required in modern air-tight homes, to prevent the gas and airflow through the water heater flue from creating an air pressure difference, which can draw gases from the water heater burner into the home. Depending on how far the direct vent needs to run, code might also require a power fan that assists the flow of exhaust gas in the vent. In older, less air-tight homes, this is rarely a problem.
If your code requires that you change from a simple atmospheric vent to a direct vent or powered direct vent, this is a more complicated job. Most people should call a pro for this work.
All plumbing installations must conform to the local plumbing code, so consult the local building department for requirements in your area. Because installation varies by location and by the type of heater, the following steps merely show the general process and may or may not apply to your situation.
Equipment / Tools
- Adjustable wrench
- Channel-lock pliers
- Tubing cutter (if needed)
- Garden hose
- Appliance dolly and straps
- Propane torch and sweat-soldering supplies (if needed)
- New water heater
- Shims (as needed)
- Plumbing fittings (as needed)
- Plumber's pipe-seal tape
- Water heater draft hood (if needed for gas heater)
- Temperature- and pressure-relief valve (if not provided)
- Water heater drain valve (if not provided)
- Vent pipe fittings (as needed)
- Galvanized plastic-lined water heater nipples (2)
- Plumbing pipe fittings as needed
- Water heater flex tubes (if needed)
- Flexible gas tube (if needed)
Shut Off the Water, and the Gas or Electricity
Shut off the utilities to the existing water heater. Turn off the water at the home's main water shutoff valve or at a branch shutoff valve controlling the cold water running to the water heater. Then, shut off the electricity or gas supply.
Drain the Water Heater Tank
Attach a garden hose to the drain valve near the bottom of the water heater. Open the nearest hot water faucet, such as in the bathroom, to prevent suction in the line that can slow the draining. Place the other end of the hose over a floor drain or run it outdoors. Open the drain valve slowly so that sediment does not clog the drain valve. Let the tank drain completely, then turn off the valve and remove the hose.
Disconnect the Water Lines
Disconnect the hot and cold water lines from the water heater, using a pipe wrench or channel-lock pliers. These may be connected to the heater with flexible tubes (typically joined with compression or union fittings) or with soldered connections (soldered lines must be cut with a tubing cutter).
Disconnect the Electrical or Gas Lines
Next, the power source for the water heater needs to be disconnected.
- Electric water heater: Remove the cover on the wire connection panel at the top of the water heater. Confirm that the circuit is off, using a non-contact voltage tester to check the individual wires, then unscrew the wire connectors joining the circuit wires to the water heater leads. Unscrew the cable clamp and remove the cable from the connection box.
- Gas water heater: Make sure the valve on the main gas line is turned off, then disconnect the gas line from the gas control valve on the water heater. This gas tube may be a flexible tube coated with vinyl, bare soft-copper tubing, or sometimes (with older water heaters) a rigid black-pipe connection.
Disconnect the Water Heater Vent (Gas Heaters Only)
Disconnect the vent pipe from the draft hood on the top of the heater. The draft hood is usually connected to the vent pipe with three or four sheet metal screws. If the draft hood is in good shape, you may be able to reuse it with the new water heater.
Swap the Old Water Heater for the New
Use an appliance dolly with straps to wheel out the old water heater and wheel in the new one. If the water heaters need to be moved up and down basement stairs, it is best to have a helper to assist you with this work. And make sure to securely strap the heater to the dolly when moving it.
Clean up the floor where the old heater was located. Move the new water heater into position, lining up the existing plumbing with the water heater's plumbing connections. Level the new water heater by shimming under the legs, as needed. If your region is subject to earthquake danger, there may be brackets or straps that need to be secured to hold the water heater in place.
Install the Relief Valve and Other Fittings
Install the various fittings required for the water heater. This always includes a temperature and pressure relief valve (TPR valve) and discharge drain pipe. Install any other fittings as needed, following the manufacturer's directions.
Connect the Water Lines
Attach galvanized plastic-lined nipples to the cold water inlet and hot water outlet openings on the top of the water heater. Installation involves wrapping the threads with plumber's pipe-seal tape, then threading the nipples into the openings and tightening them with channel-lock pliers or a pipe wrench.
Now, connect the cold water pipe to the inlet nipple on the water heater and the hot water pipe to the outlet nipple. In some cases, this can be as easy as reconnecting the flexible tubes that you disconnected when removing the old heater. But if the water pipes were hard-piped into the water heater and required cutting to remove the heater, then the job is a little more complicated.
You may need to assemble various threaded adapters, short lengths of pipe, and union fittings to join the water heater nipples to the cold and hot water pipes. How you do this will depend on the types of pipe you have and the configuration of the plumbing. It may require some sweat-soldering with a torch if you have copper pipes, but there are compression fittings, grip-fit (SharkBite) fittings, and PEX fittings that can also work with different types of plumbing pipes.
If you did not already have them, now is a good time to install flexible tubes to connect the hot and cold water pipes to the water heater. This will make it easier to disconnect the water heater should you need to make repairs or replacements in the future. This requires attaching male-threaded adapters to both the water heater nipples and the ends of the hot and cold water pipes. The flexible tubes then fit between them with coupling nuts that screw onto the adapters.
Connect Gas or Electrical Lines
Connect the gas or electrical sources, as applicable:
- Gas water heater: Connect the gas line to the gas burner control valve. Use a flexible gas line if applicable and allowed by local code. Check for leaks by turning on the gas supply valve and brushing a soapy water solution onto the gas union and all gas joints. If you see any bubbles, the connection is leaking and needs to be tightened. If you still cannot get a good seal without bubbles, call the gas company or a plumber for assistance.
- Electric water heater: Clamp the electrical cable into the wire connection box at the top of the water heater. Connect the circuit wires to the water heater leads, using wire connectors. Attach the cover plate on the wire connection box.
Reconnect the Vent (Gas Heaters Only)
Position the draft hood at the top of the water heater, centered over the exhaust opening, and slip it into the vent pipe. Secure it with sheet-metal screws. If the new water heater is a different height than the old heater, you may need to shorten the vent pipe by cutting it down to size with metal shears, or by installing a shorter pipe segment. Or, for a shorter water heater you may need to lengthen the vent by adding an additional vent pipe segment.
Make sure to connect the vent per the manufacturer's instructions and local code requirements. There should be specific parts and instructions for the new water heater. In some communities, shared venting with a chimney or flue that also serves a furnace (shown here) is no longer allowed. In this case, you may need to call a professional to reconfigure the venting for your new water heater.
Complete the Installation
Turn on a hot water tap at a remote location in the house, then turn on cold water supply valve to the water heater and let the water heater tank fill with water. You'll you'll know the tank is full when water begins to flow at the hot water tap.
For an electric water heater, restore power to the water heater circuit by turning the circuit breaker back on. For a gas heater, make sure the main gas valve is opened and confirm that the pilot igniter is working properly, following the manufacturer's directions.
Set the thermostat on the water heater to a temperature between 110 and 125 degrees Fahrenheit, as desired (120 degrees is recommended) and let the water in the tank come up to temperature.