The energy efficiency of a water heater is measured in energy Factor or (ef). The larger the number of ef, the more efficient the water heater is.

热水器能效由能量因数或(EF)来测定，EF值越大，热水器的能效就越高。

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For even greater efficiency consider buying a tankless water heater. Tankless water heaters only heat water when it is needed, instead of keeping a reserve of water at a constant temperature.

购买无水箱热水器（电热水器）是更加节能的做法，电热水器只在需要的时候对水进行加热，而不会对保存在水箱内的水加热保温。

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This paper introduces a new type of solar water-heater, which works with direct-circulate compounded form. It can raise heat efficiency.

介绍了一种全新的太阳能热水器，采用直流—循环复合工作方式，提高了效率。

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Rive could also buy a new water heater to improve energy efficiency in his home.

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Standard green features in each home include LED lighting, recycled glass countertops, a high-efficiency water heater, water-conserving fixtures including dual-flush toilets, FSC-certified bamboo flooring, EnergyStar appliances, zero-VOC paints, finishes, and adhesives, a whole-house ventilation system, low-E windows, high levels of insulation, a fully recyclable, heat-deflecting cool roof, exterior wood siding and decking made from FSC-certified cedar, and much more.

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