Piping Multiple Water Heaters: Series vs Parallel

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0 Comments Feb 23, 2015


What is the best way to pipe multiple water heaters?
We get this question quite often.

Most of the water heaters that we see out there are piped in series. We strongly recommend running water heaters in parallel, but both have their benefits and downfalls.

Piping in series is when the cold water supply enters the cold side of heater #1 and then exits out of the hot side of heater #1. Then it enters into the cold side of heater #2 then exits out of the hot side of heater #2 to feed the demand. The main concern in this setup is that heater #1 usually has a higher demand on it. We see this constantly, as the first tank usually is always first to fail. If piped in series, it is best to have the first heater set to a lower temperature then the second. This reduces the stress on the first heater. The main benefit to this setup is ease of installation and cost.

Water Heaters Piped in Series

Water Heaters Piped in Series

Image property of http://waterheatertimer.org/

Piping in parallel is when the cold water is piped in to the cold inlets of both heaters symmetrically. The water is then piped out of the hot side of each heater symmetrically as well. The reasoning behind piping the tanks symmetrically is to ensure both tanks are being filled and drawn from evenly. Both heaters should have isolation valves as well. There any many benefits to this setup, including the ability to run one heater at a time easily by isolating the other. This ensures in the event of a heater failure you will still have a hot water supply from the alternate heater. Another great benefit is maximizing output of the heaters. Piping in parallel gives you the full output of both heaters, as they are working as a team.

Example: Two 50 US gallon water heaters at 40,000 BTUs each, will now give you 100 US gallons at 80,000 BTUs.  That’s a lot of hot water!

50 US gallon John Wood water heaters piped in parallel.

50 US gallon John Wood water heaters piped in parallel.

Service, Repair, and Replacement
The Hot Water Tank Company Ltd.
www.MyHotWater.ca

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