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.


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

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

Working with supply and gas pipe

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

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

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.

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.

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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