So, before you purchase a tankless tankless water heater, it's important to know how energy efficient it is. Although, the most energy-efficient tankless tankless water heater models cost you more than the standard tankless tankless water heaters, you will benefit from its better performance that helps save on your energy bills.

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

Noritz SC-201-6M Tankless Water Heater System Control US $264.95

Tankless Water Heater Olympia 18 KW Whole House New US $205.00

American Heat AH-18 Whole House Tankless Water Heater US $391.00

TITAN N-160 SCR-3 Electronic Tankless Water Heater BRAND NEW US $309.99

Rheem RTGL74XP Outdoor 7.4 GPM Tankless Water Heater for Liquid Propane US $699.88

Bosch 1600H LP AquaStar 4.3 GPM Indoor Tankless Liquid Propane Water Heater NIB US $580.00

NIB GE INDOOR TANKLESS GAS WATER HEATER 7.5 MODEL GN75DNSRSA US $649.88

NORITZ 8 GPM INDOOR NATURAL GAS TANKLESS WATER HEATER US $1,999.99

NORITZ 8.3 gpm INDOOR HOME TANKLESS WATER HEATER NATURAL GAS NG NR83-DVC-NG US $1,319.99

NEW NATURAL GAS TANKLESS WATER HEATER 4.23 GPM / 16 L US $297.95

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

Noritz N-0751M-DVC (LP) - 9.8 GPM - 199,900 BTU/H Tankless Water Heater Propane US $910.00

Rinnai Tankless Water Heater R75LSIN Interior Natl Gas US $1,125.00

8 Valve kits for Tankless Water Heater LEAD FREE (T) US $590.00

8 Valve kits for Tankless Water Heater (S) US $460.00

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

Marey® 4.2GPM/16L Natural Gas Whole House ON DEMAND Tankless Hot Water Heater US $296.95

Rinnai Tankless Water Heater R75LSe Exterior Natl Gas US $1,090.00

Rinnai Tankless Water Heater R94LSe Exterior Natl Gas US $1,290.00

Eccotemp 40HI 6.3 GPM LP Intdoor Tankless Water Heater US $429.00

Eccotemp 40H 6.3 GPM LPG Outdoor Tankless Water Heater US $429.00

Eccotemp FVI12-LP 3.4 GPM Gas Tankless Water Heater US $269.00

Eccotemp 40H 6.3 GPM NG Outdoor Tankless Water Heater US $429.00

Rinnai Tankless Water Heater R75LSEP Exterior LP Gas US $1,090.00

Rinnai Tankless Water Heater R94LSEP Exterior LP Gas US $1,290.00

Rinnai Tankless Water Heater R94LSIP Interior LP Gas US $1,299.00

Noritz N-132M-ASME (LP) - 13.2 GPM - 380,000 BTU/H Tankless Water Heater Propane US $2,905.00

NIB Rheem Tankless Water Heater US $580.00

Bosch Tankless Water Heater ES VVT Vertical Vent Kit for AquaStar 2700ES 2400ES US $270.00

Marey Whole House On Demand 4.2 GPM Propane LP Gas 16L Tankless Hot Water Heater US $296.95

New Rheem/Paloma Tankless Water Heater 7.4 GPM Propane Gas Power Vent PTG-74PVP US $799.99

NEW Rheem/Paloma 5.3 GPM Tankless Water Heater Power Vent Propane RTG/PTG-53PVP US $529.95

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

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One important factor which can influence efficiency is the source of energy, i.e., electric, gas or solar energy. Compared to electric tankless tankless water heaters, most home owners feel that gas waters provide better performance , but then electric tankless tankless water heaters have their own advantages. Two important points in favor of electric waters heaters are their compact size and easy installation.

There is also a growing demand for solar tankless tankless water heaters due to their superior efficiency rating. You can determine the efficiency of a solar tankless tankless water heater by applying the solar energy factor (SEF).

The solar energy factor is defined as the energy delivered by the system divided by the electrical or gas energy put into the system. The higher the number, the more energy efficient. Solar energy factors range from 1.0 to 11. Systems with solar energy factors of 2 or 3 are the most common.

However for choosing a tankless tankless water heater, it may not be possible to strictly follow the consideration of energy efficiency alone. There are other factors like the size of the equipment, you requirement of hot water, availability of energy, flexibility and convenience of the heater and its overall contribution.