How to Replace a Water Heater: Tank Removal and Installation (2026)

Frequently Asked Questions

What size water heater do I need?

For a tank water heater, the first-hour rating (FHR) is the key specification — it measures how many gallons the heater delivers in the first hour of use. Sizing guide: 1–2 people: 40-gallon (FHR ~55 gallons). 2–4 people: 40–50-gallon (FHR ~65 gallons). 4–5 people: 50 gallons. 5+ people: 55–80 gallons. Also consider: if you have a soaking tub (100 gallons), you may need a 75-gallon unit or an on-demand water heater.

What is the T&P relief valve and why is it critical?

The T&P (temperature and pressure) relief valve is a safety device that opens to release water if the tank temperature exceeds 210°F or pressure exceeds 150 PSI — preventing the tank from exploding. The valve must: (1) Be installed in the designated opening on the tank, (2) Have a discharge pipe running down to within 6 inches of the floor (to prevent scalding injuries if it opens), (3) Be tested annually (lift the lever briefly — water should discharge, then stop). Never cap or plug a T&P valve.

Do I need an expansion tank?

If you have a closed system (a backflow preventer on the cold water supply), yes. When water heats, it expands — in an open system, that expansion flows back into the main supply. A backflow preventer blocks this, so without an expansion tank, pressure builds in the tank and can damage it or trigger the T&P valve repeatedly. Check: if your home has a pressure reducing valve (PRV) or a backflow preventer on the supply line, you need an expansion tank ($30–$80) installed on the cold water inlet. Most code-required installations include one.

Is water heater replacement a permit-required job?

In most jurisdictions: yes. A permit ensures the installation is inspected for proper venting (gas), electrical connections (electric), T&P valve, and expansion tank. Unpermitted water heater installations can void the manufacturer's warranty and create homeowner's insurance issues. Many areas allow homeowners to pull their own permits. The permit process is typically quick (1–5 days) and costs $50–$150.

How do I properly dispose of the old water heater?

Options: (1) Curbside pickup — many municipalities accept large appliances at the curb with advance scheduling. (2) Scrap metal yard — tank water heaters have significant steel recycling value ($10–$30). (3) Haul it yourself to the transfer station or dump — call ahead for their appliance policy. (4) Many home improvement stores or appliance retailers will haul old units when delivering new ones. Ask at purchase.

Replacing your own water heater is a significant project but saves several hundred dollars.

What you need

• New water heater (see FAQ for sizing)
• T&P relief valve (if not included with the unit)
• Flexible water supply connectors (braided stainless)
• Gas flex connector (for gas units)
• Pipe thread sealant (yellow Teflon tape for gas; white for water)
• Expansion tank (if on a closed system)
• Adjustable wrenches, pipe wrench
• Appliance dolly (for moving the old tank)
• Garden hose (to drain old tank)
• Drip pan (for placement under new unit)

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Step 1: Drain and remove old heater

1. Turn off the cold water supply to the heater.
2. Turn off heating (gas to Pilot; electric to off at breaker).
3. Connect a garden hose to the drain valve and run to a floor drain or outside.
4. Open a hot water faucet to break the vacuum.
5. Open the drain valve and let the tank drain completely (15–30 minutes).
6. Disconnect the cold and hot water supply lines.
7. Disconnect the gas supply or disconnect the electrical wires.
8. Disconnect the flue vent (gas units).
9. Move the old unit out with an appliance dolly.

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Step 2: Position new heater

Place a drip pan under the new heater location. Set the new unit in position, leaving access to all connections.

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Step 3: Install T&P valve

Thread the T&P valve into the designated port on the side of the tank using Teflon tape. Hand-tighten plus 1–2 turns with a wrench.

Install the discharge pipe (1-inch CPVC or copper) from the valve downward to within 6 inches of the floor. The pipe must not be trapped — it needs a clear path to discharge downward.

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Step 4: Connect water supply

Connect the flexible braided supply connectors to the cold inlet and hot outlet on the tank. Use Teflon tape on threads. Hand-tighten and snug with a wrench — do not over-tighten.

Install the expansion tank on the cold water line if required.

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Step 5: Connect gas or electric

Gas: Apply yellow Teflon tape to the gas pipe threads. Connect the flexible gas connector from the gas supply stub to the gas valve on the water heater. Test for leaks with soapy water after turning on the gas.

Electric: Connect the power cable per the wiring diagram on the heater (typically red to red/black to black for 240V, or match colors on 10/2 cable). Connect ground to the green screw.

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Step 6: Fill and test

Open the cold water supply valve. Open a hot water faucet in the house. Wait until water flows steadily from the faucet — this means the tank is full. Close the faucet.

Check all connections for leaks.

Restore power (electric) or light the pilot and set to normal temperature (gas).

Wait 30–60 minutes for the water to heat. Test temperature at a faucet — should be 110–125°F at the tap.

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Related guides

• How to Drain a Water Heater — annual maintenance for the new unit
• Water Heater Replacement Cost — compare DIY vs. professional cost
• Annual Home Maintenance Schedule — water heater maintenance schedule