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Thread: what is the correct water pressure

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    DIY Junior Member tilemom's Avatar
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    Default what is the correct water pressure

    Okay, in the continuing saga of trying to find out why my tankless water heater takes 5 mins to get to the upstairs shower with hot water I have found that our water pressure stinks. I measure that it takes one minute to fill a gallon jug. What is the correct water pressure supposed to be and how do I fix this?
    The baby calls me MEMMY

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    DIY Member theelviscerator's Avatar
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    Pressure and flow are two different things.

    A hypodermic needle for example can generate a lot of pressure at the tip, but almost no flow.

    Sounds like plugged lines to me.


    Disconnect the fitting right before the tankless heater (water off) then turn on full and see how fast it fills the same bucket.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    This could be entirely normal if the tankless system is only sized for say a lav faucet. In order to ensure they get the specified heat rise through them, if they have limited heat transfer, they make up by putting a restrictor in them. Sort of like waving your hand over a fire. Do it slow enough and it gets very warm over a candle. Go the same rate over a blowtorch and you'll get burned.

    What is the gpm rating on the unit you have, and does it have an externally added flow restrictor?
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member tilemom's Avatar
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    THanks fellas- I did clean the filter this morning...don't know if it made any difference as it looked very clean anyway.

    Hmm- it is a Noritz Model N-069M or N-063S. I am not sure which as one of the model numbers is for natural gas and the other for propane. WE HAVE PROPANE.

    I think it is supposed to be able to handle the whole house. So- it is either 6.9 gpm or 6.3 gpm ( like the model numbers) . I think N-069M is for propane because we have a remote controller and in the booklet it says that model does and the other model doesn't.
    Any way the capacity range is from .75-6.9 gpm.

    recovery rate of 193 gph

    is this helpful????
    The baby calls me MEMMY

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Take a bucket into the bathtub, turn the faucet to only hot, max flow and let it run for a minute. Measure how much hot water you get and let us know. That, other than probably the washing machine inlet, is the only un-restricted fixture in the house. Most tub fillers can deliver around what that unit can produce, so it shouldn't be affected by that, or if it is, not by much.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the Trades AZ Contractor's Avatar
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    Lightbulb

    Gallons per minute will depend on the temperature rise.

    If you have it set at 140 degrees and the incoming temperature is 40 degrees the unit has to heat the water up 100 degrees so it comes out slower.

    If you have the temperature set at 120 degrees and the incoming water is 80 degrees then it only has to heat up the water 40 degrees so the gallons per minute will be greater.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    While some of them have a variable heating source, I've not seen one that had a variable orafice to adjust the flow. They typically get whatever they get, and if it is too hot, they recommend a tempering valve on the outlet to prevent it from being a problem.

    Which of them has an orafice to slow the flow?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member tilemom's Avatar
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    well, finally got around to putting the bucket under the tub tap...2gallons/minute. what does that mean?

    Also, is there some way for me to increase the water pressure that we have or is that the county water people or a "real" plumber's job?
    The baby calls me MEMMY

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    Plumber BAPlumber's Avatar
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    If you think this is a pressure problem, why don't you get a pressure gauge, that connects to a hose bib, and tell us what your current pressure is?
    Brent

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    Retired Defense Industry Engineer jadnashua's Avatar
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    How old is the house, and what are the water lines made of? if the house is older and has galvanized pipe, it may be time to replace. Are you sure that all the supply valves are fully opened.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member tilemom's Avatar
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    Hmmm--house was built in 1979. I will have to get a pressure gauge...the only kind I have is for a car (LOL). I think that everything is wide open but good thought and i will check them.


    Oh- and I have wondered what the normal flow is that comes out of the tap? As I said earlier, I got 2 gallons per minute. Thanks-
    Last edited by tilemom; 10-05-2007 at 03:36 PM.
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    Retired Defense Industry Engineer jadnashua's Avatar
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    A tub filler with 1/2" supply lines should deliver somewhere around 6-7 gallons per minute. The showerhead is limited to 2.5gpm, and most sink faucets around 2.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the Trades Bob NH's Avatar
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    You need to determine what the pressure is where it comes into the house, what the supply pressure is when the flow of cold water is maybe 5 GPM, and where the pressure loss is occurring.

    It would help to have a pressure gauge on both sides of the heater.

    You should be able to operate with 40 psi, although 50 psi would be better.

    Try to measure the cold water flow at the tub. If that is high and the hot is low, then there is probably a problem with the water heater.

    If you have some kind of cartridge filter, try removing the cartridge to see if that helps the flow.

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