Introduction to tankless or on demand instant hot water heaters

Introduction to tankless, also caled "on demand" or instant or instantaneous hot water heaters

Water heating accounts for 20% or more of an average household's annual energy expenditures. The yearly operating costs for conventional gas or electric storage tank water heaters in the USA average $200 or $450, respectively.

Even if no hot water is drawn from the strorage tank of a hot water storage heater tank (and cold water enters the tank at the bottom), the heater will operate periodically to maintain the water temperature. This is due to "standby heat losses": the heat conducted and radiated from the walls of the tank---and in gas-fired water heaters---through the flue pipe becasue the xit gases remain hot. These standby losses represent 10% to 20% of a household's annual water heating costs.

One way to reduce this expenditure is to use an on demand, also called

 Tankless Water Heaters, instant or instantaneous hot water heater.

On demand water heaters are common in Japan and Europe. They began appearing in the United States about 25 years ago.

Unlike "conventional" storage tank water heaters, tankless water heaters heat water only as it is used, or on demand which means as soon as the tap is opened the heater starts up. To be able to heat the water quickly on demand the heat rating of these tankless water heaters are very high

Once activated, the heater delivers a constant supply of hot water in most cases unless too much hot water is demanded in which case the unit may reduce the temperature or flow rate or both ... remember the heater can onlt deliver a design amount of energy

They come in a variety of sizes for different applications, such as a whole-house water heater, a hot water source for a remote bathroom or hot tub, or as a boiler to provide hot water for a home heating system.

They can also be used as a booster for dishwashers, washing machines, and a solar or wood-fired domestic hot water system.

You may install a demand water heater centrally or at the point of use, depending on the amount of hot water required.

For example, you can use a small electric unit as a booster for a remote bathroom or laundry.

As an example, assume the following conditions: One hot water faucet open with a flow rate of 0.75 gallons (2.84 liters) per minute. One person bathing using a shower head with a flow rate of 2.5 gallons (9.46 liters) per minute. Add the two flow rates together. If the inlet water temperature is 50 F (10 C), the needed flow rate through the demand water heater would need to be no greater than 3.25 gallons (12.3 liters) per minute. Faster flow rates or cooler inlet temperatures will reduce the water temperature at the most distant faucet. Using low-flow shower heads and water-conserving faucets are a good idea with demand water heaters.

Using low-flow shower heads and water-conserving faucets are a good idea with demand water heaters. Demand water heaters cost more than conventional storage tank-type units.

The appeal of demand water heaters is not only the elimination of the tank standby losses and the resulting lower operating costs, but also the fact that the heater delivers hot water continuously.

Life Expectancy of tankless water heaters

Most tankless models have a life expectancy of more than 20 years. Storage tank water heaters last 10 to 15 years. Most tankless models have easily replaceable parts that can extend their life by many years more.