High incoming line pressure

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Dave2374, Apr 25, 2017.

  1. Dave2374

    Dave2374 New Member

    Apr 25, 2017

    I have 110lbs of pressure coming in my home and I believe its causing my hot water heaters relief valves to lift (I have 2 40 gallon tanks). I called the city and they said I could add a regulator inside the house or they could adjust the pressure outside at the main. I said I would just as soon install one in the house so my lawn sprinkler system isn't affected. My question is should I install an expansion tank on the hot water heater as well or is that necessary? I currently have no regulator inside or expansion tank. The house is about 15 years old, the hot water heaters are 4 years old. The incoming pressure used to be around 85, but I just measured 110 the other day. If I install an expansion tank, I read the tank needs to be set at the same pressure as the incoming main. So, what pressure is the regulator/expansion tank typically set at?
  2. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
    You need a thermal expansion tank. The sized will be larger for larger water heater, hotter WH temperature setting, and cooler incoming water. Bigger than needed won't hurt. http://www.amtrol.com/support/therm_res_sizing.html is dumbed down, but their Well-X-Trol is a top brand. http://www.watts.com/pages/support/sizing_DET.asp is a more complex calculator. Relief Valve setting is 150.

    Usually you mount them hanging down, with the pipes supporting the tank strongly supported, since the tank will be full of water at times including if the tank fails.
    Set the air precharge with the water pressure zero, to the same as the regulated pressure, or a bit higher. So if you set the PRV (pressure reducing valve) to 60, set the air to 6o to 62. To adjust the PRV, trickle water from a faucet while making adjustments. Note that PRVs will give lower pressure output at high flows-- some more than others.
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Technically, the maximum pressure in a home should be 80psi or less. Higher pressure may be beneficial on a sprinkler system, but they, also are not designed for more than 80psi.

    The T&P valves on your water heaters are designed to open at 150psi...while your nominal pressure might be 115, at night, or during other low-use times, it is not uncommon for it to spike higher. Again, your sprinkler components are not designed for more than 80psi unless they are industrial or commercial units. Once you install a PRV (or you may already have a closed system because of your sprinkler system or the city), it is very common for the water pressure to spike high enough during expansion when the WH is running to open the T&P valve.
  5. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima, WA
    Very simple. You must install a PRV and a Thermal Expansion tank. Forget about having the city reduce the water main pressure, that pressure will vary during the day and you could still have spikes. The irrigation system does not need to be reduced, so the PRV would normally be installed just in the domestic side. It is very standard for the T/P on a water heater to trip on a closed system that does not have an expansion tank unless there is a bad toilet valve that will leak the expansion unnoticed.
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