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.

Okay to use PEX to install boiler backflow device?

mossbak Member Posts: 6
Oil boiler is missing a backflow device. Was going to try to do it myself. Pex to pressure reducing valve. Not seeing any examples of backflow devices being installed with pex pipe. Is that an option or do they need rigid piping? I know backflow devices need to be horizontal to work.

Pic of current set up:

Current thought: Put in right elbow to make pex horizontal to red PRV. Crimp in two 1/2 inch male adaptors and install backflow device.

Backflow assembly here:


  • Mark Eatherton
    Mark Eatherton Member Posts: 5,840
    The BFP you are looking at is a reduced pressure zone backflow preventer, which requires annual testing and certification. Most residential applications only require a Watts 9D backflow preventer, but some jurisdictions may require it be reduced pressure zone type.

    And yes, regardless, the elbow will do the trick. Make certain it is properly supported to avoid putting excess weight on the other device, which is a single seated check valve/pressure relief valve/pressure reducing combination.

    If you go with the RZP, make sure you have a good floor drain available, because if it goes into backflow prevention, it's gonna get real wet in that room. Probably a good idea to put a single spring check up stream of it to avoid it seeing any kind of normal pressure drops.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Hilly
    Hilly Member Posts: 422
    Agreed with Mark on the 9D. If you do not have watts availanle it is a double check with atmospheric port (DCAP is the abr.) that you want on a residential boiler. Check the manufacturers literature because many can be installed in different oriebtations, which could make your install easier.
  • mossbak
    mossbak Member Posts: 6
    Unfortunately, City of Portland requires a reduced pressure zone backflow preventer, with the annoying addition of cert and annual inspections.