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Dumbest question ever.

nibsnibs Posts: 346Member
This is embarrassing to ask. Getting ready to connect the DHW, on our E50C and nowhere in the manuals can I find the max cold water supply pressure for DHW. After all the pressure concerns with the boiler/radiant side the manuals are silent.
The only clue I can find is Rinnai requires a 150psi pressure relief valve on the DHW hot side. The manual does tell what to do if the water pressure is below 22psi. I have a watts PRV that we are planning to install and would like a clue as to what pressure to set it. We are on a rural water system with wild swings from 80 to 120 psi.

Comments

  • Set your pressure reducing valve to 80 psi.

    The Uniform Plumbing Code says that's the max.
    Often wrong, never in doubt.

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  • ZmanZman Posts: 5,089Member
    edited July 1
    50-60 PSI is usually about right for a home. You should have a pressure reducing valve and backflow preventer where the water line enters the building
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • nibsnibs Posts: 346Member
    Thank you both, if smarter in my youth should have taken up the plumbing and gas fitting trade, instead of chasing girls.
  • STEVEusaPASTEVEusaPA Posts: 3,189Member
    edited July 1
    nibs said:

    Thank you both, if smarter in my youth should have taken up the plumbing and gas fitting trade, instead of chasing girls.

    You could’ve done both 😀
    If you’re putting in a backflow preventer, and you should, make sure you also install a portable water expansion tank with the pressure set the same as the pressure reducing valve.

    -Not a dumb question at all.

    steve
  • Jamie HallJamie Hall Posts: 10,893Member
    Don't forget that if you do have a pressure reducing valve and/or backflow preventer on your domestic water, you also need an expansion tank...
    Jamie

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • hot_rodhot_rod Posts: 11,790Member
    edited July 1
    I recommend a dhw expansion tank on any water heater, good chance some day a BFD will be installed if it is public water.

    For small capacity tankless and plate HX type combis this is a tank often used.

    45 psi is the common set pressure on PRVs from the factory, 45- 50 precharge on dhw exp tanks.

    The E50C manual show this pressure spec, 14- 40 psi.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • nibsnibs Posts: 346Member
    @hot_rod , Now I am really embarrassed, there it is right in the manual.
    Your screen shot is for the boiler, next line down is DHW and correct me if wrong, shows a max of 150 psi. 10 bar.
    Will set the PRV to 60 to be gentle to the system, with check valve and expansion tank.
    Again thanks to all.
  • I've installed pressure reducing valves on houses that have 100 psi down to 80 psi with owner's responding, "Where'd the pressure go?"

    People like their water pressure high, especially if they have a pull-out spray faucet in the kitchen with a flow restrictor. Maybe that's a western phenomenon.
    Often wrong, never in doubt.

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  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,658Member
    House I grew up in had 80psi city water. It was great for the restricted galvanized potable system. When I replaced it with copper it was like a waterfall.
    Serving Northern Maine HVAC, and Controls
  • hot_rodhot_rod Posts: 11,790Member
    Sure, you can have what ever water pressure you want :)

    80 psi is what toilet, faucet, plumbing fixtures suggest as max. operating pressure. UPC & ICC suggests 15- 80 psi in their code.

    I think it comes down to whatever you are use to or comfortable with. Same with heating and cooling thermostat settings

    Some low flow shower heads at 80 psi feel more like acupuncture.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • nibsnibs Posts: 346Member
    @hot_rod , what amazes me is that you found the pressure limit minutes after I posted, and I have been going through the manual several times and missed it. Thank you.
  • hot_rodhot_rod Posts: 11,790Member
    nibs said:

    @hot_rod , what amazes me is that you found the pressure limit minutes after I posted, and I have been going through the manual several times and missed it. Thank you.

    sheer luck on my part. I use Supplyhouse.com for current tech literature, they do an excellent job keeping current manuals and make it easy to find.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • HenryHenry Posts: 914Member
    We had low water pressure a few months ago. We had 70PSI and great flow for 34 years. I called the city. They checked for a water entrance leak. They then gave me a new water meter. Problem solved. Most hot water tank manufacturers now require an expansion tank to have a warranty. We install an expansion tank on all of our replacement or new installs.
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