Sizing a domestic water heater system constitutes an art form more than an exact science. For anything other than a small residential system, you cannot simply go to a table or chart and make your selection. Codes provide only generalizations such as “Hot and cold water shall be supplied to all sinks, lavatories, showers, etc.� They do not indicate how much hot water is required. Codes do, however, give information about pipe materials and minimum and maximum flow rates to fixtures (combined cold and hot water), and they address safety concerns such as maximum temperatures and required safety devices.
A number of factors must be considered when sizing a system, and experience plays a big part. Every system is different, so the path that leads to final selection is also different. Two buildings can be physically the same (i.e., have the same number of fixtures), but the quantity of water required may be different if the buildings will be occupied by different groups of people. For instance, an apartment building for older people would have a different use profile than one that primarily houses families.
Information Gathering
So how do you size and select a domestic hot water system? The first step is to collect the information needed to define the system parameters and narrow the options. Some of the information will be