Installing an On-demand Water Heater

On-Demand Water Heaters

Long popular in Europe, on-demand (or tankless) water heaters provide hot water seconds after turning on the faucet.

A compact on-demand unit can be tucked into a cabinet or closet. It costs more than a standard water heater but uses less energy, so it may pay for itself in a few years.

It heats 3-5 gallons per minute, plenty for a dishwasher or a shower, but probably not enough for both at the same time.

Installing one calls for running gas lines and supply lines and installing a vent. A gas unit is shown here; electric units are also available.

Checklist

Time
At least a day to run a gas line, install a vent, and connect plumbing for an on-demand water heater

Tools
Drill, screwdriver, groove-joint pliers, tools for running water supply and gas lines, tin snips

Skills
Working with supply and gas pipe

Prep
Go over your plans with an inspector to make sure the installation will be safe.

Materials
On-demand water heater, gas pipe and fittings, supply pipe and fittings, vent pipe and fittings

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Step 1

Install the water heater in a code-approved location. The manufacturer's specifications determine acceptable distances between the unit and vent pipes and combustible surfaces. Make sure the room is well-ventilated. Mount it using the hardware provided.

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Setting Water Temperature

When you first use the unit, turn the gas valve switch off and wait for five minutes to clear out any gas (check the manufacturer's specific instructions). If you smell gas, test for leaks. Once you are sure there are no leaks, turn the switch on and turn on the hot water of a nearby faucet. An automatic spark will light the pilot light, which will fire the burner. After 10-30 seconds, the pilot will go off while the burner remains on. Turn on the faucet's hot water to maximum flow; wait a minute for the water to reach maximum heat. Turn the temperature dial counterclockwise to lower the heat and clockwise to increase the heat. If incoming water becomes colder in the winter, you may need to turn up the dial to achieve the desired temperature.

Step 2

Attach the pressure regulator, which ensures safe flow of gas to the unit. Run an approved gas line. Use 3/4-inch pipe for any runs more than 10 feet; 1/2-inch pipe can be used for shorter runs. Connect the line to the regulator, turn on the gas, and test for leaks.

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Installing Vent Piping

The water heater must be vented to the outside of the house in a code-approved manner, using flue pipes at least 5 inches in diameter (follow manufacturer's instructions). For the flue to draw efficiently, maximize the vertical rise -- it should be at least 6 feet -- and use as few elbows as possible. Test the flue before using to make sure it draws.

Step 3

Copper is recommended for the water supply pipe, at least for 3 feet before and after the water heater. Install a pressure-relief valve (some manufacturers provide it) before the ball valve on the outgoing hot-water line.

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