Installing Multiple Water Heaters

Multiple water heater installations are predominantly for commercial or industrial applications where a high capacity of heated water may be required during peek times; however some residential homes may also benefit if they have large volume fixtures such as a jetted tub or hot tub. When designing a potable water system, great care must be taken to fully anticipate the current and future demands of heated water. If you need help determining the expected hot water requirements check here- A.O. Smith's sizing guide for commercial hot water applications.

Multiple water heaters can be installed in two primary methods that are very similar; series connections and parallel connections, each having its own benefits and drawbacks depending on the desired result.

Connecting Water Heaters in Series

Four water heaters connected in seriesWhen water heaters are connected in series it means the cold water is fed through each tank; one after the other, with the first tank's hot outlet becoming the next tanks cold inlet. Under normal conditions the first tank in the series will do most of the heating. Under high demand situations the first tank will not be able to sufficiently heat the water so the next tank in series would begin operation, and the next...until the water is up to temperature.

Points to consider when connecting water heaters in series are:

  • A bypass must be installed so that any malfunctioning tank can be removed while keeping the system operational.
  • Different styles / models of water heaters can be used in series but the tank with the highest BTU rating should be fed first.
  • Pipe size is limited by the tanks inlet and outlet.
  • The system operates efficiently under both low and peek demands.
  • No requirement to balance the piping as with a parallel installation.

Connecting Water Heaters in Parallel

Unlike in a series connection, the water supplied and distributed by a parallel connection is evenly balanced causing all the tanks connected in parallel to share the workload. The piping arrangement to and from parallel connected water heaters are extremely important to ensure the water is evenly distributed and does not take the path of least resistance (short circuit).

Two parallel connected water heaters Four parallel connected water heaters

Points to consider when connecting water heaters in parallel are:

  • A bypass in not required as any malfunctioning tank can be isolated and removed while keeping the system operational.
  • All tanks connected in parallel must be of the same type, model and rating to function properly.
  • Pipe size is not limited by the tanks’ inlet and outlet as headers can be increased in size.
  • The system operates efficiently under both low and peek demands.
  • More labor/material intensive to create balanced distribution.