How to Replace Hot Water Heaters

Adjusting the water temperature is the final step in a water heater retrofit.

Like all plumbing components, a water heater is subject to corrosion and mineral deposit build-up, and there comes a time when it no longer functions properly and must be replaced. Whether your heater is gas or electric, it's common for the plumbing fittings connecting it to be also worn out, and you may have to replace them when you replace the heater. It will make the retrofit easier if the new heater is the same size as the old one. If not, you may have to add extra pipes for plumbing, gas and venting.

Things You'll Need

• Garden hose
• Screwdriver
• Wrenches
• Pipe cutter
• Torpedo level
• Blocks
• Vent hood
• 2 copper unions
• Soldering supplies
• 2 copper male adapters
• 1/2- or 3/4-inch copper pipe
• Flexible copper tubing (optional)
• 2 brass nipples
• Pressure relief valve
• Copper elbow
• Black iron pipe

Instructions

1. Turn off the electricity or the gas to the old heater and give the water about 12 hours to cool down. Attach a garden hose to the outlet on the bottom of the heater and run it to to a sink, drain or outdoors. Open the valve and let the water drain.

2. Turn off the breaker controlling the heater if it is electric, then open the electric panel on the heater and disconnect the wires with a screwdriver. If the heater is gas, turn off the gas valve and unscrew the union joining the heater to the gas line with a wrench. Remove the vent hood and swing the vent line away.

3. Unscrew the unions or flexible connectors joining the heater to the water lines with a wrench. If the lines are joined by solid piping and there are no unions, cut through the pipes with a pipe cutter. When the pipes are disconnected, walk the heater outside and dispose of it.

4. Walk the new heater into position and place it so that the gas inlet or electrical panel, as well as the water lines, are facing in the right directions. Place a torpedo level on top of the heater and place blocks under the heater or adjust the legs as needed to make the heater level.

5. Install a new vent hood on a gas heater -- don't reuse the old one -- and connect it to the vent line. The hood has clips that fit into slots on the top of the heater.

6. Connect the water supply. If the old heater was connected with unions, replace them by cutting them off and soldering on new ones. Solder male adapters to the ends of two short lengths of 1/2- or 3/4-inch copper pipes -- depending on the size of the water supply lines -- and screw them into the inlets on the top of the heater.

7. Solder pipes and fittings together to reach the existing lines. Terminate the pipes with the other halves of the unions and make the final connections by screwing the unions together. If the supply pipes terminate with threaded male connectors, you can join the heater to them with flexible copper tubing, screwing the ends of the tubing to the water lines and the heater. You may have to screw brass nipples into the inlets in the top of the heater if they aren't there already.

8. Hook up the power to an electric heater by removing the panel cover and connecting the wires. The red and black wires connect to the brass terminals, the white wire to the silver one and the bare or green wire to the green one.

9. Screw one half of a black iron union to a length of black iron pipe that will reach the gas line if you are connecting a gas heater. Screw the other half of the union to the gas line, if there isn't one connected already. Screw the pipe into the gas inlet and join the pipes by screwing the union together.

10. Install a pressure relief valve by screwing it into the threaded inlet on the top of the heater. Connect a length of copper pipe to the valve that reaches the edge of the heater, solder on a 90-degree elbow and another length of pipe that reaches to within a few inches of the floor. This overflow tube is a safety precaution that will protect you from scalding if the valve suddenly opens.

11. Open the cold water valve and let the tank fill. This may take an hour or so. When the tank is full, turn on the breaker to start an electric heater or turn on the gas valve and light the pilot to start a gas one.

Tips & Warnings

• Wrap plumbing tape around all threaded connections before you screw them together.

• If you are installing an electric heater, check the electric meter when you turn on the breaker. If the heater is working, the meter should be spinning faster than it was before you turned it on.

• Check for gas leaks after making gas connections by spraying liquid soap around the connections and watching for bubbles. Leaking gas lines are an explosion and fire hazard.

References

• This Old House; How to Replace a Water Heater; Richard Trethewey
• Aubuchon Hardware: How to Replace a Water Heater