Recirculating Pump or Point of Use tank?

Discussion in 'General Plumbing Help' started by bowens, Jun 6, 2019.

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  1. Jun 8, 2019 #41

    bowens

    bowens

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    how, in a closed pipe system, is the water gonna move any faster without increasing the pressure? going from 1gpm to 16gpm...isn't that quite a bit of pressure increase?
     
  2. Jun 8, 2019 #42

    RenewDave

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    What’s your point?....exactly....
     
  3. Jun 8, 2019 #43

    bowens

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    without preheating, I'm not understanding how the hot water is gonna get to the faucet any faster.
     
  4. Jun 8, 2019 #44

    RenewDave

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    RECIRCULATION!!!!!!??????!!!!!????!!!!!! Wow! It’s not rocket science.
     
  5. Jun 8, 2019 #45

    bowens

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    maybe it is, if you can't explain it
     
  6. Jun 8, 2019 #46

    frodo

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    maybe if I type real slow?

    your hot water heater heats the water. do you understand how that happens?

    the hot water heater tank is full of hot water,

    Their is a pipe that is connected on the bottom of the water heater,,OR it can connect at the top on the hot water pipe

    I prefer using the lower connection..

    this pipe goes under floor ALLLLLLLLLLLLLLLL the way over to the KS we are going to call this line P1
    WHERE It comes up through the floor and connects to the hot water supply pipe under the kitchen cabinet
    Where P1 connects to the supply line under the cabinet,,A TEE is installed
    Another pipe we will call R1 connects to this tee.
    R1 follows P1 both are routed next to each other back to the water heater
    R1 connects to the COLD water pipe on top of the water heater
    A CHECK VALVE is installed on the cold pipe

    2.jpg

    we have finished installing the loop
    on S1 next to the water heater, A pump is installed..Its orientation is pumping AWAY from the water heater

    You were asking about PRE HEATING the water.. your water heater does that, its heats water, that is why it is called a "WATER HEATER"
    when the pump turns on, the water inside the water heater, is pumped to the KS
    through the tee under the cabinet and is pumped back to the heater in the pipe R1
    where it enters the water heater through the cold water pipe on top of the heater
     
  7. Jun 8, 2019 #47

    RenewDave

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    Fuckin rocket science!!!!! Oh no, just plumbing! Easy peasy!
     
  8. Jun 8, 2019 #48

    frodo

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    plumbing is Latin for common sense
     
  9. Jun 10, 2019 #49

    bowens

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    you guys are good at drawing schematics (and congratulating yourselves), but not at fluid dynamics. The following statement came from Grundfos:

    The pump does not increase any pressure but circulates the water. If there is no water movement then the water cools and takes time to reach the faucet like it did prior to the pump.
    [​IMG]
     
  10. Jun 10, 2019 #50

    frodo

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    1] ... I never said that the pump increases pressure...
    2]...you are correct it circulates the water.

    3].. This is where you do not understand the conversation or are not comprehending how it works

    The water in the pipe that is not moving is cold, [undisputed truth]
    when the pump turns on,
    the water , inside the pipe is circulated back into the water heater
    at his time, the water inside the pipe is NOW HOT WATER
    According to the pump I submitted, pipe size and length of run from pump to the KS
    the wait time for hot water at the sink will be approx.4 seconds from the moment the pump is activated
    TrumpWallGif.gif
     
  11. Jun 10, 2019 #51

    bowens

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    Grundfos says 30 seconds or however long it takes now (unless the water is preheated, of course). So there must be something that you're not understanding, probably having to do with closed pipe systems.
     
  12. Jun 10, 2019 #52

    SGkent

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    They are in the SF bay area. Need I say more.
     
  13. Jun 11, 2019 #53

    frodo

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    regale us with your wisdom, clear up my misunderstanding with facts
     
  14. Jun 11, 2019 #54

    bowens

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    in a closed system, the ability to move water at a higher rate will require more pressure and/or more volume. Since the volume is restricted by the pipe, then it would have to be pressure. Recirculation pumps don't provide that kind of pressure, and you wouldn't want that kind of pressure in a residential system, anyway.
     
  15. Jun 11, 2019 #55

    frodo

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    It is not a closed system,,it is fed by the city water supply typical psi of 50-60
    with out a prv ..which makes this an open system..
    with out the pump. the pressure at the sink from the water heater would be in the neighborhood of 50 psi
     
    Last edited: Jun 11, 2019
  16. Jun 11, 2019 #56

    bowens

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    it's essentially a closed system because there's nothing to accommodate an increase in volume, aside from opening a tap. Also, I have a prv.
     
  17. Jun 11, 2019 #57

    frodo

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    An open system is open to the atmosphere. Like an out door wood boiler also a hot water tank is considered open system.

    A closed system is like an indoor boiler with a boiler feed that is pressurized to the pressure you need to rise the water to the given height you need ( top floor )

    On a closed system you are able to use black pipe or cast Iron boiler or steel. Any oxygen getting in to the system ( usually by adding new water )
    will corrode the pipe, pumps, boiler.

    Any time a system has new water going into it all of the time .... it is considered open.

    Water has oxygen it in..... once that is boiled the oxygen comes out of the water.

    open a faucet, the system is an open system.

    BACK. to the subject
    with this OPEN system, and the fact it is pressurized by city water at 60+-psi
    The damn water will be hot at the KS faucet seconds after the circulating pump kicks on
     
  18. Jun 11, 2019 #58

    bowens

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    you say that, but the pump mfg says not. I don't have the math to prove anything, so I'm gonna go with my limited understanding of pipe flow and what they said. I don't see how the hot water is gonna move that much faster without a significant pressure increase.
     
  19. Jun 11, 2019 #59

    PlumbGate

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    Wow so many comments! I will tell you from experience as I have a water circulation pump. I have a large house and each end of the house used to take close to 4-5 minutes for hot water to come out. After putting in the circulation pump, it takes like 20 seconds. I put 2 "tee" thermostats in my house, one at each end, both in upstairs bathrooms literally the farthest point from each other and the water heater in the basement. This allows the kitchen at one end to also get hot much faster and a 1st floor powder room on the other end. I could not be happier with the circulation pump. It is on a builtin timer that I set to turn off at night so hot is there when I need it. It is truly set and forget I installed it over 2 years ago and haven't touched it since.
     
  20. Jun 11, 2019 #60

    PlumbGate

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    Huh? There is no added pressure. The pump slowly circulates the water using a motor. It pushes it through the pipes from the hot water heater to the sink on the hot side to the under-sink thermostat. If the thermostat calls for it, it opens a path between the hot and cold water back to the water heater.
     

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