住宅供暖是美国住宅中使用效率最低的能源之一。为了更好地了解现场性能，在明尼苏达州的10户家庭中安装了24台天然气热水器（8台单一流行型号的储水式热水器和16台9种不同型号的瞬时热水器）。在15个月的交替模式测试过程中，对热水器进行了广泛的监测和测试。与储水式热水器相比，九台非冷凝式瞬时热水器使用的能量减少了22%至54%，平均每年节约57特姆（6.0 GJ/年）。与储水式热水器相比，七台冷凝式瞬时热水器使用的能量减少了28%至63%，平均每年节省74特姆（7.8 GJ/年）。尽管瞬时热水器可以大幅减少水加热能源的使用，但其高昂的安装成本是当前能源价格的主要障碍。 测量的年度热水器效率也与美国能源部（DOE）的能源系数（EF）进行了比较。两种类型的瞬时热水器的实测年效率比其EFs低约10%，而储水式热水器的年效率比其EF低19%，这表明这两种类型的热水器的相对性能没有很好地用EF指标来表征。引文:内华达州拉斯维加斯ASHRAE Transactions第117卷第1部分

Residential water heating is one of the least efficient energy uses in residences in the United States. To gain a better understanding of in situ performance, 24 natural gas water heaters (eight storage water heaters of a single, popular model and 16 instantaneous water heaters of nine different models) were installed in ten Minnesota homes. The water heaters were extensively monitored and tested under an alternating mode test procedure for 15 months. The nine noncondensing instantaneous water heaters used 22% to 54% less energy than the storage water heater, saving an average of 57 therms/yr (6.0 GJ/yr). The seven condensing instantaneous water heaters used 28% to 63% less energy than the storage water heater, saving an average of 74 therms/yr (7.8 GJ/yr). Even though instantaneous water heaters can substantially reduce water heating energy use, their high install cost is a major hurdle at current energy prices. Measured annual water heater efficiencies were also compared to the U.S. Department of Energy (DOE) energy factor (EF). Measured annual efficiencies of both types of instantaneous water heater were about 10% lower than their EFs, while those of the storage water heater were 19% lower than its EF, suggesting that the relative performance of these two types of heater is not well characterized by the EF metric.