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RPZ backflow prevention

Steve Minnich
Steve Minnich Member Posts: 2,680
Qualifier - I'm not a plumber.

Why is that some municipalities require them and others don't?

Do most of you feel that they are the way to go no matter what? Or, are there grey areas?

They're a pain for me logistically. I have to sub out a licensed plumber who is RPZ certified.
Steve Minnich
Minnich Hydronic Consulting & Design, LLC
[email protected]
Paul S_3


  • Jamie Hall
    Jamie Hall Member Posts: 17,164
    I have no idea what the current codes are on the subject. My own opinion -- and the one which I cheerfully enforced when I was in the plumbing inspection business, several careers ago, is that it's a grey area. I required them where there was a potential toxic problem on the downstream side, and when there was a reasonable chance the the downstream pressure could be higher at times than the supply. The code I was working from at the time -- NPC in the 70s -- was less flexible; if there was stuff you didn't want to drink downstream, you had to have one, regardless of pressure differences.

    I agree that they are a bit of a nuisance nowadays -- back then, any licensed plumber could install them. Which may or may not have been a good thing, since people didn't maintain them anyway...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Steve Minnich
  • hot_rod
    hot_rod Member Posts: 15,065
    Yeah the codes and more the local inspectors are all over the board on BFDs. In some areas of NY a basic dual check is acceptable, without the atmospheric port!?

    In some areas only RPZ.

    The choice of devises used to be based on the hazard level of the fluid. As such only ethylene glycol systems would need protection. Water and PG are GRAS generally regarded as safe.

    I see the inspectors side as they have know way of knowing what is in the system, mixed glycols, older inhibitors with chromates, various blends of hydronic inhibitors. Car antifreeze gets used by DIYers sometimes etc.
    Some of the early solar thermal systems had Bray oil as the fluid.

    So to protect the local AHJs and the liability of the jurisdiction, they tend to lean towards RPZs.

    It seems easier to go along with them than arm wrestle over fluids, pressures, back flow potential.
    But it does bring in the rectification issue, and testing them sometimes leads to leaks and the need to rebuild. Ugh.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Steve Minnich
  • Captain
    Captain Member Posts: 25
    Eliminate the requirement for a backflow prevention device (BPD) and the connection to the domestic water supply completely by installing a System Pressurization unit (Glycol Feeder). If your not connected to the domestic water supply then the code doesn't apply.
  • Steve Minnich
    Steve Minnich Member Posts: 2,680
    @Captain - Good point! I put LWCO's on them all anyway.
    Steve Minnich
    Minnich Hydronic Consulting & Design, LLC
    [email protected]
  • SWEI
    SWEI Member Posts: 7,356
    I'm another fan of no permanent connection to the potable water supply at all. The Axiom boxes are great, though on smaller systems we just upsize the expansion tank. We leave a double female (washer) hose long enough to reach from a nearby hose bibb to the nearest drain valve on site. If we get a call from an LWCO trip, we walk them through the process, which buys us a few days to get there.
    Steve Minnich
  • delta T
    delta T Member Posts: 863
    edited August 2016
    You still have the possibility of a leak in a dhw coil though...

    I think most AHJs that require bf devices will worry about that possibility and possibly require one on the main water into the house to prevent spread to the municipal water supply no? Here they are required on the domestic supply to any buildings with more than one residence and all commercial.
  • Captain
    Captain Member Posts: 25
    Having an RPZ on the fill valve won't prevent cross contamination through a leaking DHW coil. Having a system pressurization unit (glycol feeder) will limit the amount though. Only the contents of the feeder tank will be pumped into the system and through the leaky DHW coil. If there is a fill valve connected, the entire contents of the system could potentially be pushed into the domestic water supply.

    But honestly, what are the chances of that happening in a residential system with a 30psi relief valve. Domestic water supply pressures are much higher than hydronic system pressures. If there's a leak the domestic water will flow into the hydronic system, blow the relief valve (30psi) and push the contaminated water onto the floor.