What is a Tankless Hot Water Heater?

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  • Written By: Josie Myers
  • Edited By: Andrew Jones
  • Last Modified Date: 25 May 2020
  • Copyright Protected:
    Conjecture Corporation
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A tankless hot water heater, also called an instantaneous, or demand water heater, is an appliance that heats water as it runs through incoming pipes. They are praised for their energy savings and are considered part of a home plan for "greening." Standard versions are available for use with gas or electric energy.

Water heaters with a tank have been the residential standard for decades. These heaters hold water at a warm temperature while waiting for use and therefore use energy when it isn't necessary. Tankless water heaters were created to remedy this waste. In order to encourage their use, the federal government offers a tax rebate for any home using a tankless hot water heater.

An electric tankless hot water heater uses an electric element to heat the water. The water enters the unit, is warmed by the element and goes to the faucet or appliance hot. Some electric heaters can serve an entire house, but the most common type serves a specific appliance or room. For example, the heater may be located right below the feed line for a shower or dishwasher.

When choosing a gas tankless hot water heater, there are two options: natural gas or propane. This type of tankless hot water heater requires a vent to the outside, usually through a wall or the roof, depending on the setup of the home and location of the heater. Usually, a gas tankless hot water heater is larger in size than an electric one and can heat water at a higher rate than its electric counterparts. The one downfall to them is that a pilot light usually is required, a necessity that increases wasteful fuel burn.

Some units are unable to keep up with the demands of a household. Running a shower, dishwasher and clothes washers at the same time may result in overload and cause cold water to flow. This can be somewhat remedied by using larger "whole house" units, or by adding smaller units for specific appliances. Smaller units are also popular for their ease of use with everything from outdoor barbecues to pool showers.

When choosing a tankless hot water heater, it is important to carefully research the specifications of the system. One of the most important things to know is the temperature requirements for the home. Standard incoming temperatures should be taken, and a desired temperature decided upon. Find the difference between the incoming temperature and the desired outgoing temperature. This difference is the "rise," so called because it tells how many degrees the temperature needs to rise in order to fit the needs of the home.


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