How to Replace a Water Heater? [Step-by-Step Guide]

Replacing a water heater is a big job. It involves water lines, venting and either gas or 240-volt wiring, so only attempt it if you are qualified, or hire a licensed plumber or electrician. Ask your local building department about permits and inspections before you start.

You need the right tools, plumbing skills and, for most homes, gas-fitting or electrical skills. A mistake can mean a gas leak, a scald, or exhaust fumes in the house from bad venting.

If you don’t have any experience, it is highly recommended to call a professional. Both HVAC and Plumbing companies replace and repair water heaters. Occasionally, local handyman companies do as well. For a sense of the cost, This Old House’s installation cost guide, updated in June 2026 with Home Depot data, says basic tank models start at about $1,200 installed and tankless units average around $2,800.

Removing the Old Water Heater

1. Turn off power at the breaker panel (if electric) or shut the gas off (if gas). For an electric heater, confirm with a voltage tester that the power is really off
2. Close the cold water valve
3. Drain the water heater (do this by attaching a garden hose to the drain and opening the drain valve or drain screw). The water can be very hot, so run the hose to a drain or outdoors
4. Open the hot water faucets in your home
5. Disconnect the water lines
   1. If you have flexible lines, you can just loosen the fittings
   2. If you have rigid copper pipe, you will have to cut it free with a tubing cutter
6. Disconnect the electrical (if electric) or disconnect the gas line (if gas). Only do this if you are qualified to work on gas lines and 240-volt wiring, or hire a licensed plumber or electrician
7. Disconnect the vent from the top of the water heater, and check the new heater’s manual for which venting parts you can reuse
8. Wait for the water heater to drain, and then remove it

Installing the New Water Heater

1. Line the new water heater up with the water lines
2. Attach the water lines
   1. If using flexible lines, you will simply need to apply pipe tape and tighten the fittings
   2. If using rigid copper piping, you will have to solder the connections. You will need to get some fittings from the hardware store to attach the lines. You’ll need a fitting that screws onto the water heater, a section of straight pipe, and a coupling for each side. Solder these with solder made for drinking water pipe, and flux. If you have not soldered pipe before, hire a licensed plumber
3. Attach the gas line (if gas) or connect the electrical (if electric)
   1. When using a gas line, you will want to use a pipe thread sealant rated for gas to ensure a leak-free connection, or hire a licensed plumber to make the gas connection
4. Reconnect the vent
5. Open the water lines
6. Before the power goes on, open a hot faucet and let the tank fill until the water runs steadily with no air. An empty tank burns out the heating elements. Then turn the power on (if electric) or turn the gas on (if gas)
   1. Check for gas leaks using a small container of soapy water and a paintbrush or makeup brush. Shake up the soap until it is frothy and soap up around the fittings. If you see any bubbles, you have a leak: turn the gas off at the valve and have a licensed plumber fix it. If you smell gas, leave the building and call your gas supplier from outside
7. If your heater has a pilot light, light it. There will be instructions on the water heater that show you how.
8. Check all the water connections for leaks, and turn the hot water faucets off once they run steadily

Remember: the tank needs time to heat. A. O. Smith says a 40 to 50 gallon gas tank takes about 30 to 40 minutes to heat fully and an electric tank 60 to 90 minutes, so you won’t have hot water right away!