Demand Water Heaters
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On-demand or tankless water heaters heat water only when it is being used in the home, rather than heating the water and storing it in a tank. The most common water heaters used in the U.S. include a storage tank that holds hot water until it’s needed. The standby heat loss – when no one is using hot water – from this storage tank can account for 10 to 30 percent of your water-heating costs.
The advantages of demand water heaters over storage water heaters include the fact that they have no standby losses – since there is no storage tank – and they provide nearly instant hot water if they are installed near the fixtures they serve.
If your water heater is installed a long way from your sinks and showers, you are already in the habit of waiting for hot water. This situation is worst when the piping runs through a cold concrete slab. Waiting for hot water wastes both energy and water. If you have a well, your well pump also runs longer to replace the water that goes down the drain while you wait. To avoid this waste, a small on-demand water heater can be installed right in the kitchen or bathroom, and will provide nearly instant hot water without the wait. Larger demand heaters, to serve an entire home, can be installed in the same place as your current storage heater, though this location doesn’t provide instant hot water like under-the-sink units.
If a demand water heater makes sense in your home, it’s best to consider changing it out now before your current storage water heater fails. That way, you’ll have time to get competitive bids and shop for a unit that suits your home and habits. The largest electric demand water heaters will supply a single fixture such as a shower or sink but are still a demand problem for electric utilities because of the large amount of power they draw. Gas demand water heaters feature larger capacities than electric models and can serve more fixtures. All demand water heaters are smaller than the storage heaters they replace, so they can fit in your bathroom, basement, or utility room.
For gas or propane on-demand water heaters, prefer sealed-combustion units. Conventional tank-storage water heaters are a safety problem because of their weak chimney draft. The sealed-combustion water heater provide greater combustion safety along with much greater energy efficiency.
The Homeowners Handbook to Energy Efficiency contains simple, practical energy-efficiency ideas for saving on water heating costs