On Demand Water Heaters
Tankless tankless water heaters are also known as on demand water heaters or instantaneous water heaters. It is because they provide hot water only as it is needed. Unlike conventional storage water heaters, on demand water heaters don't produce the standby energy. That means, by using on demand water heaters you are going to save money on energy consumption and bills. It will be interesting to know how they work and whether a demand water heatermight be the ideal one for your home and what the criteria for selecting a tankless water heater.
When you switch on the heater, cold water flows in one end of a pipe, flows through and around several curved pipes over the heating elements, which is paced at the top of the heater and out the other end as hot water. Beneath the heating unit, there is a typical sink setup. The sink has two pipes coming out the bottom, one for the hot water line and one for the cold water line. Both pipes lead to the heating unit, which is installed in close proximity to the area of hot water use, and is connected to a power source (110 or 220 volts).
Demand water heaters heat water directly without the use of a storage tank. So there is no loss of standby heat losses . When a hot water tap is turned on, cold water travels through a pipe into the unit. Either a gas burner or an electric element heats the water. As a result, demand water heaters deliver a constant supply of hot water. You don't need to wait for a storage tank to fill up with enough hot water. However, a demand water heater's output limits the flow rate.
 8 Valve kits for Tankless Water Heater LEAD FREE (S) US $590.00 
|
 8 Valve kits for Tankless Water Heater (T) US $460.00
|
 Rinnai Tankless Water Heater R94LSIN Interior Natl Gas US $1,299.00
|
 Rinnai Tankless Water Heater R75LSIP Interior LP Gas US $1,125.00
|
 HHP HH19 Single Shower Tankless Water Heater US $434.12
|
 HHP HH28 Tankless Water Heater Whole House US $704.95
|
 HHP HH12 Single Shower Tankless Water Heater US $412.47
|
 Stiebel Eltron Tankless Water Heater Tempra 12B US $435.00
|
Typically, demand water heaters provide hot water at a rate of 2–5 gallons per minute. Gas-fired demand water heaters produce higher flow rates than electric ones. . For example, taking a shower and running the dishwasher at the same time can stretch a demand water heater to its limit.
To overcome this problem, you can install two or more water heater connected in parallel for simultaneous demands of hot water. You can also install separate demand water heaters for appliances such as a clothes washer or dishwater that use a lot of hot water in your home.