Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

expansion tank location with tankless heater

I'm installing a noritz tankless dv hot water heater with noritz's hot and cold isolation/pruge valves. Since the valves attach to the tankless with half unions there is no place between the cold valve set-up and the tankless to cut in an expansion tank.

Should I then install the expansion tank between the prv and the iso/purge valve set-up. I have always been under the belief that the expansion tank should be installed before the cold water shut-off incase the valve is closed it would still absorb any expansion without activating the prv.


  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited January 2012
    I wouldn't put one in....

    It's a tankless, which means it won't be firing unless a tap is open. Expansion tanks are there to allow the expansion to be absorbed. You won't have any expansion to speak of, because if the burner is on, a tap is open. When the tap is closed, the burner is off.

    Save your money for something else.


    There was an error rendering this rich post.

This discussion has been closed.