“总体系统效率”的定义与1976年ASHRAE手册——Systemsvolume中的定义不同。为了获得这样的效率，即“在使用点输送的水的热量与提供给加热器的热量之比”，有必要在每个水龙头上安装热量表。显然，这不是一个实际的提议。因此，本文中报告的效率将略高于“整体系统效率”，因为我们忽略了这样一个事实，即使用点处的水温度将低于离开加热器的温度，这是由于连接水龙头的供水管道冷却。 现场测试表明，在有限使用的情况下，在供水温度达到循环温度之前，有必要运行多达14 L（.3.6 U.S.gal）的废水。引文:研讨会，ASHRAE交易，第86卷，第一部分，加利福尼亚州洛杉矶

The "Overall System Efficiency" definition is not the same as the defined in the 1976ASHRAE Handbook--Systemsvolume.To obtain such an efficiency, which is defined as the "ratio of the heat in the waterdelivered at points of useto the heat supplied to the heater," it would be necessary to fit heat meters to every faucet. Obviously, this is not a practical proposition. The efficiencies reported in this paper will consequently be somewhat higher than the "overall system efficiency" since we are ignoring the fact that the water at point of use will be at temperatures lower than that leaving the heater due to cooling in the supply pipework to the faucets. Spot tests showed that at times of limited use it was necessary to run as much as 14 L (.3.6 U.S. gal) of water to waste before the supply water temperature reached the circulating temperature.