Dumbest question ever.

nibs

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.

Alan (California Radiant) Forbes

Set your pressure reducing valve to 80 psi.

The Uniform Plumbing Code says that's the max.

Zman

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

nibs

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

STEVEusaPA

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.

Jamie Hall

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...

hot_rod

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.

nibs

@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

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.

Solid_Fuel_Man

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.

hot_rod

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.

nibs

@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

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.

Henry

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.