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.

Stiebel Eltron Temptra 12 Tankless Water Heater US $400.00

American Heat 16 KW Whole House Tankless Water Heater US $269.00

Rheem EcoSense Tankless Natural Gas Water Heater Plus Remote ECO180DVN3 NIB US $999.99

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Bosch Pro Tankless C 1210 ESC NG - Tankless Water Heater - Best Price!!! US $1,619.99

Noritz Tankless Natural Gas Water Heater N-075M1 US $400.00

EZ 202 - Tankless Water Heater LP (Liquid Propane). 3.2 GPM + FREE Mfg Warranty US $264.95

NATURAL GAS NG TANKLESS WATER HEATER 16L, 4.23 GPM US $297.95

NORITZ TANKLESS WATER HEATER LONG 4" DIRECT VENT KIT US $209.99

NORITZ TANKLESS WATER HEATER SHORT 4" DIRECT VENT KIT US $289.99

Bosch Pro Tankless C 1210 ES - Tankless Water Heater - Best Price!!! US $1,529.99

AQUAH INDOOR ON-DEMAND PROPANE GAS TANKLESS WATER HEATER 12L, 3.2 GPM US $249.95

AQUAH INDOOR ON-DEMAND PROPANE GAS TANKLESS WATER HEATER 16 L, 4.23 GPM US $329.99

AQUAH INDOOR ON-DEMAND NATURAL GAS TANKLESS WATER HEATER 16 L, 4.23 GPM US $299.99

AQUAH INDOOR ON-DEMAND NATURAL GAS TANKLESS WATER HEATER 12L, 3.2 GPM US $249.95

NEW RINNAI RV53eN - NATURAL GAS TANKLESS WATER HEATER US $549.00

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Tempra 24 Stiebel Eltron Tankless Water Heater US $609.00

Tempra 20 Plus Stiebel Eltron Tankless Water Heater US $685.00

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TITAN N210 SCR4 TANKLESS WATER HEATER FREE FEDEX US $420.00

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Bosch Thermo 660 EF NG - Tankless Water Heater - Best Price!!! US $719.99

Titan Tankless Hot Water Heater - N-85 Digital Model US $205.00

ON-DEMAND LPG PROPANE GAS TANKLESS WATER HEATER 16L, 4.23GPM US $297.95

LPG PROPANE GAS TANKLESS WATER HEATER 3.2 GPM, 12 L US $269.95

ON DEMAND NATURAL GAS TANKLESS WATER HEATER 3.2 GPM, 12L US $269.95

Rheem EcoSense 8.4 GPM 180,000 BTU Natural Gas Indoor Tankless Water Heater US $888.88

AQUAH 16L (4.23 GPM) ON-DEMAND PROPANE LPG GAS TANKLESS WATER HEATER NEW US $299.99

AQUAH 16L (4.23 GPM) ON-DEMAND NG NATURAL GAS TANKLESS WATER HEATER US $299.99

AQUAH ON-DEMAND NATURAL GAS NG TANKLESS WATER HEATER,12 L, 3.2 GPM US $249.95

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Girard Tankless Water Heater With Outside Door US $350.00

Rheem 6.4 GPM Outdoor Tankless Natural Gas Water Heater US $900.00

Bosch GWHC800ESNG Tankless Water Heater Natural Gas US $1,495.00

Tankless Water Heater Olympia 24 KW Whole House New US $225.00

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GAS TANKLESS WATER HEATER - DIRECT VENT - WHOLE HOME US $394.95

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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.