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Dumbest question ever.

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nibs
nibs Member Posts: 511
in THE MAIN WALL
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.

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  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,002
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    Set your pressure reducing valve to 80 psi.

    The Uniform Plumbing Code says that's the max.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    rick in Alaska
  • Zman
    Zman Member Posts: 7,569
    edited July 2019
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    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
  • nibs
    nibs Member Posts: 511
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    Thank you both, if smarter in my youth should have taken up the plumbing and gas fitting trade, instead of chasing girls.
    Solid_Fuel_Man
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited July 2019
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    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 Hall
    Jamie Hall Member Posts: 23,282
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    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...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,131
    edited July 2019
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    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
    Living the hydronic dream
  • nibs
    nibs Member Posts: 511
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    @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.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,002
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    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.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    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 & Controls. I burn wood, it smells good!
  • hot_rod
    hot_rod Member Posts: 22,131
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    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
    Living the hydronic dream
    Solid_Fuel_ManVoyager
  • nibs
    nibs Member Posts: 511
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    @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_rod
    hot_rod Member Posts: 22,131
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    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
    Living the hydronic dream
    STEVEusaPASolid_Fuel_Manrick in AlaskaCanucker
  • Henry
    Henry Member Posts: 998
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    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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