How to Replace a Water Heater

  • 01 of 10


    Residential Water Heater
    Residential water heaters can be either gas or electric. Julia Nichols / Getty Images

    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 size, although you can usually change the size a bit — for example, from 40 to 50 gallons, provided there is enough room for the heater. 

    Note: 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. 

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  • 02 of 10

    Shut Off the Water and Gas or Electricity

    water meter shutoff
    Shut off the water main at the water meter.

    Shut off the utilities to the existing water heater. Turn off the water at the home's main water shutoff valve or the shutoff valve at the cold water supply line running to the existing water heater. Then, shut off the electricity or gas supply:

    • Electric water heater: Turn off the circuit breaker on the water heater's circuit at the home's breaker box. This is typically a 30-amp, double-pole breaker.
    • Gas water heater: Turn off the gas supply at the shutoff valve on the gas pipe nearest the water heater. 
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  • 03 of 10

    Drain the Water Heater Tank

    Inside of gas hot water heater, drain valve
    The drain valve is located at the bottom of the water heater. Dorling Kindersley / Getty Images

    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. 

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  • 04 of 10

    Disconnect the Water Heater

    Pipe wrench
    A pipe wrench may be needed to disconnect plumbing connections. Jan Stromme / Getty Images

    Disconnect the hot and cold water lines from the water heater. These may be connected to the heater with flexible hoses (typically joined with compression or union fittings) or with soldered connections (soldered lines must be cut with a tubing cutter). Then, disconnect the gas or electricity:

    • Electric water heater: Confirm that the circuit is off to the water heater, using a non-contact voltage tester, then disconnect the wiring connections and circuit cable from the water heater. 
    • Gas water heater: Confirm that the gas supply is shut off at the shutoff valves, then disconnect the gas line to the water heater. Disconnect the vent pipe from the draft hood on the top of the heater.
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  • 05 of 10

    Remove and Replace the Water Heater

    Plumber Installing a Water Heater
    Install the water heater. Jim Zuckerman / Getty Images

    Have an assistant help load the old water heater onto the appliance dolly and remove the old unit. 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.  

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  • 06 of 10

    Install the Relief Valve and Other Fittings

    Temperature and pressure relief valve
    Temperature and pressure relief valve.

    Install the various fittings that come with 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.

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  • 07 of 10

    Connect the Water Pipes

    Add a shutoff valve to the cold water supply if it does not already have one. Connect the cold water inlet and hot water outlet on the water heater to the cold and hot water pipes. Be sure to use the correct type of fittings. Some connections often include a dielectric union to prevent an electro-galvanic action called electrolysis, which leads to premature corrosion of the metals. Flexible connections are helpful if the inlet and outlet do not line up exactly with the old plumbing. If you must use soldered connections, have the connections made by a plumber. 

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  • 08 of 10

    Connect the Gas or Electricity

    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: Connect the circuit wires to the water heater leads in the electrical junction box on the heater unit. Circuit wiring is usually housed in flexible metal cable or conduit where it connects to the water heater. 
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  • 09 of 10

    Attach the Vent (Gas Water Heater)

    Gas vent run from water heater to chimney
    Comstock / Getty Images

    Attach the vent pipe to the draft hood on the water heater (for gas water heaters only). There should be specific parts and instructions for the new water heater. Connect the vent per the manufacturer's instructions and local code.

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  • 10 of 10

    Set the Water Heater Temperature

    Hand Turning Down Water Heater Thermostat
    Turn the heater on and set the water heater temperature. BanksPhotos / Getty Images

    Get the new water heater running with the following steps, as applicable:

    1. Turn on the cold water supply valve to the water heater and turn on the water supply valve (or the house water supply, as applicable). Let the water heater tank fill with water: turn on a hot-water faucet in a remote bathroom or the kitchen; when water comes out of the faucet, the tank is filled (the water will be cold).
    2. Restore power to the water heater circuit, for an electric heater. 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. 
    3. Set the thermostat on the water heater to a temperature between 110 and 125 degrees F, as desired (120 degrees F is standard) and let the water in the tank come up to temperature.