by Daniel J. Gansle

Created on: June 10, 2008

Tankless water heaters are becoming increasingly popular due to their ability to conserve energy. But just what is a tankless water heater, and how can it heat water if there's no tank?

Traditional hot water heaters collect water in a large tank and heat it. These must keep the water at a certain temperature, all day, every day; thus the heater's elements are working quite often. When hot water is used in the home, for example after a shower, the hot water heater must refill with water and heat it up again. So you can see just how much energy is consumed just by heating and maintaining hot water on a daily basis.

Maintenance is also an issue with traditional hot water heaters. Experts recommend frequent draining of the water heater in order to expel sediments that collect in the bottom of the unit. Doing so ostensibly increases the energy efficiency of the water heater, though in my own experience I'm not so sure it made much of a difference. In areas with higher mineral content water, internal corrosion of the water heater can also become a problem that reduces energy efficiency.

Tankless water heaters work by heating water as it passes through the unit, which is typically mounted on the side of the home. The energy savings are substantial as the unit turns on only when a faucet opens looking for hot water. There's no water to heat, and no continuous temperature to maintain. This Old House plumbing and heating contractor Richard Trethewey explains: "Because you are heating water as you need it, it is "tankless," also called instantaneous. They work beautifully and are made of stainless steel, so they last. The up side is that you could shower for 24 hours straight."(1)

You can purchase either an electric or natural gas tankless water heater. Energy savings for natural gas are up to 30 percent, while electric units might see a savings of up to 70 percent over traditional water heaters. One brand of tankless water heater even comes with a remote control digital thermostat which allows you to instantly adjust the hot water temperature from anywhere in the home.

In the past, flow rates for tankless hot water heaters were minimal and allowed only one hot water use in the home at a time. But these days, you can purchase a higher gallon per minute (GPM) tankless heater that instantaneously heats up to 7.4 gallons per minute; adequate for two to three hot water applications in the home at a time (e.g., two showers and the kitchen sink).

Tankless hot water heaters are more expensive than traditional ones, but the energy savings over time will most certainly pay for itself.

Source Notes:
1. Richard Trethewey, "Tankless Hot Water Heaters," This Old House, 2007 Time, Inc.
http://www.thisoldhouse.com/toh/asktoh/question/ 0,213064,00.html

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