How to Replace a Water Heater
Switch out an old, inefficient water heater for a new unit
When replacing a water heater, it's important to know the size of the tank and whether it operates on gas or electricity.
Professional installation can add $150 to $450 to the cost of replacing a standard tank-style water heater, so some experienced DIYers look to the possibility of installing it themselves, though it's important to note that this is not a project for beginners. Replacing a water heater will require the DIYer to make both plumbing connections as well as wiring or gas hookups, plus a vent connection if for homes with a gas heater. Find out how to replace a water heater.
Warning
All plumbing installations must conform to the local plumbing code, so consult the local building department for requirements in your area. Since installation varies by location and by the type of heater, the following steps merely show the general process. This project is best left to professionals.
What You'll Need
Equipment / Tools
- Adjustable wrench
- Channel-lock pliers
- Tubing cutter (if needed)
- Screwdrivers
- Garden hose
- Appliance dolly and straps
- Propane torch and sweat-soldering supplies (if needed)
Materials
- New water heater
- Shims (as needed)
- Plumbing fittings (as needed)
- Plumbers pipe-seal tape
- Water heater draft hood (if needed for a 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)
- Water heater flex tubes (if needed)
- Flexible gas tube (if needed)
Instructions
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Turn Off Water and Fuel Source
Turn off the water at the home's main water shutoff valve or at the isolation valve on the incoming cold water line.
- For an electric water heater: Turn off the electricity running to the unit by switching off the corresponding circuit breaker.
- For a gas water heater: Turn off the gas supply at the shutoff valve nearest the water heater.
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Drain the Water Heater Tank
Attach a garden hose to the drain valve near the bottom of the water heater and place the other end of the hose over a floor drain or run it outdoors. Open the nearest hot water faucet, then open the drain valve slowly and allow the tank to drain completely before turning off the valve and removing the hose.
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Disconnect the Water Lines
Disconnect the hot and cold water lines using a pipe wrench or channel-lock pliers for compression or union fittings. Use a pipe cutter to disconnect water lines with soldered connections.
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Disconnect the Electrical or Gas Lines
Next, the power source for the water heater needs to be disconnected.
- For an electric water heater: Remove the cover on the junction box at the top of the water heater. Unscrew the wire connectors and cable clamp to disconnect the water heater.
- For a gas water heater: Use a pipe wrench or channel-lock pliers to disconnect the gas line from the gas control valve on the water heater.
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Disconnect the Water Heater Vent (Gas Heaters Only)
The draft hood is usually connected to the vent pipe with three or four sheet metal screws. Use a screwdriver to disconnect the vent pipe from the draft hood.
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Swap the Old Water Heater for the New
Switch the old and new water heaters using an appliance dolly. Have a second person help move the units up and down the stairs. Clean the floor, then move the new water heater into place, ensuring that the existing connections line up with the water heater's connections. Level the new water heater by shimming under the legs, as needed.
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Install the Relief Valve and Other Fittings
Install the temperature and pressure relief valve (TPR valve) and discharge drainpipe, as well as any other fittings as needed, following the manufacturer's directions.
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Connect the Water Lines
Wrap the threads of two galvanized plastic-lined nipples with plumber's tape, then thread the nipples into the cold water inlet and hot water outlet openings on the top of the water heater using channel-lock pliers or a pipe wrench.
Depending on the configuration of the plumbing, you may just need to reconnect the flexible tubes by screwing them onto the galvanized nipples. However, in most cases, you will need to prepare new pipe assemblies to reconnect the water lines.
- Measure the distance from the top of the water heater to the hot and cold water lines.
- Cut two lengths of copper pipe to the correct length.
- Solder FIP adapters to the base of each pipe assembly.
- Connect the pipe assemblies to the cold water inlet and hot water outlet.
- If done correctly, the new pipe assemblies should line up with the cold and hot water lines. Complete these connections by soldering in dielectric unions, which allow the pipes to be disconnected without cutting or soldering in the future.
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Connect the Gas or Electrical Lines
Connect the gas or electrical sources, as applicable:
- For an 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.
- For a gas water heater: Connect the gas line to the gas burner control valve and 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.
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Reconnect the Vent (Gas Heaters Only)
Position the draft hood at the top of the water heater over the exhaust opening, slide it into the vent pipe, and secure it with sheet metal screws. Make sure to refer to the manufacturer's instructions and local code requirements. There should be specific parts and instructions for the new water heater.
If the new water heater is taller than the old unit, shorten the vent pipe by cutting it down to size with metal shears, or by installing a shorter pipe segment. For a shorter water heater, lengthen the vent by adding an additional vent pipe segment.
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Complete the Installation
Set the thermostat and turn on the cold water supply valve to refill the water heater. You will know the tank is full when water begins to flow from the hot water tap that was opened at the beginning of the job.
- For an electric water heater: Restore power to the water heater circuit by turning the circuit breaker back on.
- For a gas water heater: Make sure the main gas valve is opened and follow the manufacturer's directions to confirm that the pilot light igniter is working properly.
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 connecting the existing flue and draft hood to the new heater, though there are factors (such as pitch and draft of the connections) that make the process much more complicated than it seems. When done incorrectly, exhaust gases (including carbon monoxide) can remain inside the home, which is why this project is best left to professionals.
The building code in some communities may require changing to a different means of venting if 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 and 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 the local code requires a 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.