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April 18, 2014  |  Login
Lose the Tank: More Efficient Water Heaters
By Dan Chiras

Travel through Europe and other parts of the world, like Japan, where energy is expensive and efficiency is a cultural norm and you won’t find a storage water heater like the ones in North American homes.

In such regions, the tankless water heater is the technology of choice. Why?

Because tankless water heaters outperform their conventional counterparts easily by 20 percent or more. Like storage water heaters, tankless water heaters provide hot water on demand but they do so without storing huge quantities of hot water. In fact, as their name suggests, they have no storage capacity at all.

Anatomy of a Tankless Water Heater

Tankless water heaters for household use are attractive, compact units that mount on the wall in a central location in our homes or near the main hot water demand centers. The heart and soul of all tankless water heaters is a device called a heat exchanger—a combustion chamber in which cold water is quickly brought up to temperature (Figure 3-2b). The heat exchanger transfers heat from the burner to the water, heating it instantaneously. A flue pipe vents unburned gases and pollutants like carbon monoxide out of the house.
Here’s how a tankless water heater works: when hot water is required—for example, when someone turns on a hot water faucet—a water flow sensor in the tankless water heater sends a signal to a central control module in the unit. This tiny computer, in turn, sends signals to an electronically controlled gas valve in the gas manifold. The valve opens and allows natural gas or propane to flow into the combustion chamber of the heat exchanger. The gas is ignited by a pilot light or by a spark froman electronic ignition device. Cold water flowing through the pipe in the heat exchanger is immediately brought up to the desired temperature. As soon as the hot water faucet is turned off, however, the water flow through the water heater ceases and the flame goes out. The net result is that you heat only the water you need at any one time.


                            Cutaway of a tankless water heater
Under-the-Sink Water Heaters

Many tankless water heaters in use in Europe fit under the sinks of homes and apartments. They heat water for one sink only and are typically powered by electricity. The household-sized units described in this chapter are centrally located so they can service all hot water needs in a home. They are often powered by natural gas or propane, both of which are much more efficient fuel options than electricity.

Pros and Cons of Tankless Water Heaters

Tankless water heaters cost more than their conventional counterparts and are a bit more challenging to install. (This isn’t a job for most do-it-yourselfers.) However, they do provide significant advantages over storage water heaters. As just noted, they heat only the water needed at any one moment. As a result, they are usually at least 20 percent more efficient than standard water heaters. That means they provide the same amount of hot water as a storage water tank, but use 20 percent less fuel. Utility bills will be 20 percent lower, too.
Because there’s no standby loss, they also produce less waste heat. In the summer, that means less internal heat gain and lower cooling bills.

Another huge advantage of tankless water heaters is that they outlast conventional water heaters. more



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