two water heaters, new whole house filter, max 90 psi, can I use one Expansion tank?

Discussion in 'Water Heater Forum, Tanks' started by Ed P, Jun 10, 2014.

  1. Ed P

    Ed P New Member

    Messages:
    4
    Location:
    California
    Two water heaters, one house, other for detached garage washing machine. Never had expansion tanks installed.

    Re piped and added whole house water filter system with bi-pass. Max psi rating is 90 psi for water filter canisters.

    City pressure 145 psi, regulator set at 65 to 70 psi. (measured)

    Each water heater can take closed house/garage system to 140 psi (measured).

    Can I install a single very large Expansion tank anywhere in the cold water loop to cover both water heaters? Or must I have large individuals closely to each water heater?


    Since each water heater is 40 to 60 gallons and max press needs to be at or less than 90 psi, individual expansion tanks are going to be 10 gallon (water volume, actual tank volume about 2 times that). Heafty size for installation locations.
  2. Reach4

    Reach4 Active Member

    Messages:
    1,944
    Location:
    IL
    You can have a single expansion tank as long as neither water heater is separated from the expansion tank by a checkvalve or a regular valve that might be closed. That probably means you need two expansion tanks.
  3. Ed P

    Ed P New Member

    Messages:
    4
    Location:
    California
    No check valves but of course there are isolation valves at each of the two water heaters. Joy to do both. Thanks for quick response.
  4. Reach4

    Reach4 Active Member

    Messages:
    1,944
    Location:
    IL
    Thinking about it, I guess those valves would only be closed when the associate water heater is off. So with that in mind, I now think one tank would do it.

    Not a pro.
  5. Terry

    Terry Administrator Staff Member

    Messages:
    14,819
    Location:
    Bothell, Washington
    A properly sized expansion tank works for system. They don't need to be at the water heater location, just within the system.
    Any check valve would take it out of the system. Sometimes when water heaters have recirc lines, they also have checks.
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