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  2. Energy factor - Wikipedia

    en.wikipedia.org/wiki/Energy_factor

    The energy factor metric only applies to residential water heaters, which are currently defined by fuel, type, and input capacity. [5] Generally, the EF number represents the thermal efficiency of the water heater as a percentage, since it is an average of the ratio of the theoretical heat required to raise the temperature of water drawn to the amount of energy actually consumed by the water ...

  3. Water heating - Wikipedia

    en.wikipedia.org/wiki/Water_heating

    A BTU is the energy required to raise one pound of water by one degree Fahrenheit. A US gallon of water weighs 8.3 pounds (3.8 kg). To raise 230 L (60 US gal) of water from 10 °C (50 °F) to 50 °C (122 °F) at 90% efficiency requires 60 × 8.3 × (122 − 50) × 1.11 = 39,840 BTU. A 46 kW (157,000 BTU/h) heater, as might exist in a tankless ...

  4. Energy conversion efficiency - Wikipedia

    en.wikipedia.org/wiki/Energy_conversion_efficiency

    Energy conversion efficiency depends on the usefulness of the output. All or part of the heat produced from burning a fuel may become rejected waste heat if, for example, work is the desired output from a thermodynamic cycle.

  5. Hot tub - Wikipedia

    en.wikipedia.org/wiki/Hot_tub

    A 5-seat hot tub with a cast acrylic shell, supported by a frame structure, showing vents for water circulation and massage Outdoor hot tubs. A hot tub is a large tub full of water used for hydrotherapy, relaxation or pleasure. Some have powerful jets for massage purposes. Hot tubs are sometimes also known as "spas" or by the trade name Jacuzzi ...

  6. Thermal efficiency - Wikipedia

    en.wikipedia.org/wiki/Thermal_efficiency

    An electric resistance heater has a thermal efficiency close to 100%. [8] When comparing heating units, such as a highly efficient electric resistance heater to an 80% efficient natural gas-fuelled furnace, an economic analysis is needed to determine the most cost-effective choice.

  7. Heating seasonal performance factor - Wikipedia

    en.wikipedia.org/wiki/Heating_seasonal...

    The higher the HSPF rating of a unit, the more energy efficient it is. An electrical resistance heater, which is not considered efficient, has an HSPF of 3.41. [3] Depending on the system, an HSPF ≥ 9 can be considered high efficiency and worthy of a US Energy Tax Credit. [4]