Well pump > two water heaters > recirculation - sanity check

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by John_NC, Dec 16, 2006.

  1. John_NC

    John_NC New Member

    Dec 16, 2006
    Great forum! This site comes up all the time as I have been researching my new house plumbing design.

    First off, we are a family of 5, with 3 pre teen children. I took on GC-ing our new home. It's been a slow process but it is a big project by my standards anyway.

    We are on well water. The well was a disappointment, went 300 ft, got 3 gpm, told them to keep going to try for more. after 525' total depth, I ended up with 3.5 gpm. Not great but adequate for house use.

    The house has 6 full bathrooms and two laundry rooms on three levels, basement, 1st and 2nd. I chose to go with a hot water recirculation pump and put the hot water heaters on the basement.

    For the well, I selected a Grundfos 10gpm 1.5 hp constant pressure pump. I realize the pump can outpump the well's recovery rate but it has an auto-shutoff dry running feature and setting it at 500', the maximum it can output at that depth is 3 gpm so I don't think it's possible to run the well dry. It's a matter of performance.

    I created a spreadsheet and charts based on my well, this pump, assumed psi setting. The color chart is my calculation of how long I can run at various flow rates, minimum to maximum. Green is optimal performance, yellow is marginal, red, unacceptable. I plan to set my pump to provide 70psi to assure good pressure to the upstairs baths. I might cut it back to 60 if necessary. With the Grundfos SQE pump, it's supposedly very easy to adjust, just a push of a button.
    I am assuming the pressure will drop as the well approaches the yellow but flow will remain relatively constant. As it approaches the red < 30psi, flow will undoubetly suffer until a tap is closed allowing pressure to build.

    The graph is the performance curve with various psi settings, 0, 30, 40, 50, 60 and 70. This is what I used to calculate sustained flow durations.

    I'm not 100% sure any of this is correct, Does my theory of well pump operation and performance, pardon the pun, "hold water"?


    1st sanity check - I assume the peak SUSTAINED use rate will be in the neighborhood of 5-10 gpm. Normal peak use would be 1 shower, 1 bath and 1 washing machine running simultaniously, say 10 gpm for up to 30 minutes. According to my calculations, I can go 60 minutes at 10 gpm before pressure drops from my anticipated setting of 70 psi.

    2nd sanity check - I have a 3/4" hot water loop and 3/4" cold supply through the house. I wish I had gone with 1" but sheetrock's up and I'm thinking (hoping) the limiting flow factor here is probably the well supply. The pipe is pex. I pretty much expect to see a degrade in pressure/flow if I have any more than 3 outlets running at the same time. but at 70 psi, I'm hoping 4 at one time will be usable.

    3rd sanity check - I purchased 2 80 gallon hot water heaters (electric) and a circulation pump. I plan on hooking them up in series. I think this will be the only way to fly with the hot water loop.

    Well guys? What do you think? Am I screwed or am I on the right track? Feel free to punch holes in any or all of my setup. I ask the so called experts and get a different story every time I ask.

    Thanks for your feedback in advance.

  2. leejosepho

    leejosepho DIY scratch-pad engineer

    Nov 23, 2006
    disabled-retired industrial fabricator
    200 miles south of Little Rock
    Maybe I missed something, but from where might the additional 1.5-6.5 gpm come? I am curious about what the true experts might say here, but I would be inclined to suggest the purchase and use of a water tanker parked at the side of the house. 3.5 gpm will take a full minute just to get enough water in a bucket to wash the car while everyone in the house waits in turn to flush any one of the six toilets or to attempt to draw a little bath water ... or, maybe you could cut your pressure way back to ration what actually is available ...
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  4. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    You do not mention a storage tank, but without one you will have to depend on the water in the well only. That water will be a combination of the water standing in the well above the pump and the inflow, so the diameter of the well and the standing water level will be important. Once that water is gone, and the pump outruns the inflow, you will be out of water.
  5. Master Plumber Mark

    Master Plumber Mark Master Plumber

    Feb 6, 2005
    Sensitivity trainer.. plumber of mens souls
    indianapolis indiana - land of the free, home of
    gpm dont matter --its VOLUME you want

    from some past experiences, it really
    did not matter how much gpm you had comming into the
    house ......

    of course MORE is better--- but you get what you get
    and then throw the fit...

    it was ALWAYS the size of the bladder holding tank that either
    made or broke the systems performance.....

    we have a few customers that opted to put TWO large
    WELL-X-TROLLS commercial sized bladder tanks into their
    mechanical room and hooked them up in parrellel with one
    pressure switch....

    this seemed to give them ---MUCHO Volume--- before it would have to
    kick in ---- it was the only way to tolerate things

    the problems that they were having was the
    pressure balanced DELTA shower and tub faucets on
    the second floor would go wackey when the VOLUME and pressure
    began to drop dramatically...

    If I understood you right.....
    I dont hink trying to torque up your recirualtion line
    is a great idea at all....and I dont see why you would want to
    its just going to confuse those pressure balanced faucets

    in fact its best to just get a TEEL pump with a timer on it and
    set it to run at 7 am for a few minutes, 12 pm, and 5pm...

    all you will do is wear out your heaters quicker and eat up your
    wallet and copper recirualtiojn lines...

    it would be wise to make sure that all t he showers in the home
    are water saveing types

    Their are others that would know more about this than me, and
    you will also have a pressure drop across your water conditioner to
    factor into the equation too...

    I know that their is a way to put an extra 100 gal holding tank with a
    BOOSTER PUMP in the basement
    above and beyond the 2 bladders to really increase the volume
    and pressure
    something like that they have to do in large buildings to pump the water up 25 floors...

    you need a large mass of storage VOLUME to really make your big house perform right.

    and its going to cost you some extra big bucks .

    Just tell your wife you that this is her X-mas present....
    Last edited: Dec 17, 2006
  6. John_NC

    John_NC New Member

    Dec 16, 2006
    Well stores 1.5 gallons per foot

    I neglected to mention, the static water level in my well is 35' from the surface. I used 40' for my calculations to round off. There are 1.5 gallons per foot of well depth. The one advantage to a deep well is the storage it can provide. I plan to set the pump at about 500'
    Storage calculation:
    (500 - 40) * 1.5
    = 690 gallons of storage.

    By the time I get down to the last 15 gallons of storage (490'), the flow will be equal or less than the well's production rate of 3.5 gallons per minute according to the pump specifications. (see the chart) and that's with no pressure so it shouldn't be possible run the pump dry.


    So if we are using 10 gpm, I calculated the storage at the depth where the pump performance drops below acceptable pressure (30 psi), in this case,

    300' - 40' (static depth) = 260 foot
    X 1.5 gal per foot storage in well
    = 390 gallons available to me at 10 gpm with usable pressure

    Now I calculate the storage "burn" rate
    10 gpm used - 3.5 gpm well replenish rate
    = 6.5 gpm

    Simple division of the available water by burn rate
    = 60 minutes of continious consumption at 10gpm

    I'm taking this as a worse case scenario, I think 10 gpm is a lot of water to use for a straight hour, opinions?

    Here's a more realistic stab at the pumps worst hour scenario.

    Pressure washer 4gpm for the full hour = 240 gallons
    Shower#1: 2.5 gpm for 20 minutes = 50 gallons
    Shower#2: 2.5 gpm for 20 minutes = 50 gallons
    Master shower 5 gpm for 20 minutes = 100 gallons
    1 Washing machine load (front load) = 20 gallons max
    Miscelanious toilets, sinks, another 20 gallons

    I do realize the pump can't do 3 showers, a 4 gpm pressure washer 9 toilet flushes and a wash load at the same time but according to my chart, I should have that amount availabe to me at 10-12 gpm flow rate for the full hour.

    Here's how I figured it:
    adding up total consumption = 480 gallons in 60 minutes = an average rate of 8 gpm

    During that hour, the well has replenished 210 gallons at 3.5 gpm.

    Total water drawn from well storage would be: 480 - 210
    = 270 gallons.

    At this point let's say consumption drops to a resonable level, anything below 3.5 gpm, my storage replenishes, use above 10 gpm would peter out in about 20 minutes (deservedly so, I think)

    When the well came in at 3.5 gpm, irrigation went out the window. I do not plan to water the lawn with this well. I might install a rainwater recovery tank for that in the future but that's another topic.


    Last edited: Dec 17, 2006
  7. John_NC

    John_NC New Member

    Dec 16, 2006
  8. Master Plumber Mark

    Master Plumber Mark Master Plumber

    Feb 6, 2005
    Sensitivity trainer.. plumber of mens souls
    indianapolis indiana - land of the free, home of
    Bigger is always better.....

    you certainly have some impressive numbers
    that are way, way above my head......

    I dont even want to think about trying to factor in
    all these numbers anymore.....

    What did the well driller tell you ???
    have you not found a good well man in your area???

    if you literally almost have nothing comming
    out of that well it might be wise to go with some sort of
    LARGE systern out in the yard ........

    You are the guy that has built this 6 bathroom house,
    with two laundry rooms ......right??
    that has to be costing you some big bucks........

    and you are nuts if you think this is going to perform correctly...

    Now that you are up to your neck in it
    its wise not to skimp on this well at all
    or you will probably live to regret it..

    I dont care what your numbers are telling you

    you are the one that has to listen to your wife when she
    screams and hollers about substandard performance..

    It sounds like yoiu are building a beautiful mansion--dream houise

    get a few "well men" in your area to give you an estimate
    for what will really work for years and years

    Last edited: Dec 17, 2006
  9. John_NC

    John_NC New Member

    Dec 16, 2006
    Am I skimping?

    Mark, I respect your status as a sr member here but do you think 3.5 gpm is literally nothing?

    Why am I nuts if I think my set-up won't work? This is why I'm here, to get informed opinions.

    I have gotten confirmation from a reputable "well man" in the area but on the same token, he originally recommended a standard pump with a cycle stop valve (CSV) to provide me with steady pressure. to the tune of a $7k+ pricetag.

    I thought that was a bit expensive for a well pump and started researching the recommendation to mainly see what kind of ride I was being taken for. I called the mfr of the CSV and quickly determined this was a poor option.

    With the pump he recommended, and the well full up at static 35', the high pressure side would have been 235psi on that valve, way out of tolerance for the recommended 125 psi differential from high to low. the valve would have failed within weeks. Also, there would have been a 25psi friction loss across the valve effectively reducing my well storage utilization by 86 gallons.

    I pointed this out to the guy, he admitted, the set-up was ill advised. He had used the CSV valves before but not on a 1.5 hp pump.

    I fail to see where I'm "skimping". Please tell me what you would install if you were me, I'm all ears. I guess I could install a battery of 2 or 3 120 gallon bladder tanks that would add some storage.

    From my research so far, a constant pressure pump would perform better as far as minimal pressure fluctuations, ease of use, flexibility and not to mention economy.

    The reason I'm building this house myself is because I CAN'T afford it any other way. It's UNREAL what people will try to get away with charging. There are a few trades that are competetive but more often than not, folks pull up, see the kind of house you're building and price their bid accordingly. I have had more than one vendor admit they price their jobs at "what they think the owner can afford".

    BTW the parts for this system will run me about 1,800 including wire and pipe. Even at $125/hr to have a professional come out and install it, my cost should be less than 3k.
  10. Master Plumber Mark

    Master Plumber Mark Master Plumber

    Feb 6, 2005
    Sensitivity trainer.. plumber of mens souls
    indianapolis indiana - land of the free, home of
    Post To The Well Forum

    It might be wise to post this informaiton
    to the well forum....their are many other fellows
    that know more than me..

    My opinion is no better than any one elses....

    I do service plumbing and tangle with wells occasionally

    good luck
  11. John_NC

    John_NC New Member

    Dec 16, 2006
    Lifting the kimono

    To fill in the full picture...
    This is all the plumbing I can think of and the reason I feel it's essential to have a tight pressure tolerance.
    5 hose bibs
    Laundry - Washer connections
    Bathrooms, 4 - 3 shower tubs, 1 shower, 4 toilets
    Main floor:
    Kitchen - 2 sinks, ice maker, dishwasher
    Family room, wet bar sink
    Garage - slop sink
    Laundry - slop sink, washer connections
    Bathrooms - 1 full, 2 halfs - 4 sinks, 3 toilets, 1 big whirlpool tub, 1 double head shower
    Wet bar - dishwasher, sink, ice maker
    Bathrooms, 1 full 1 half - 3 sinks, 1 shower

    A pressure tank set-up would fluctuate 15 to 20 psi between cut on anf off pressures unless I went with a higher end variable setting pressure switch (not a problem) but would cause short cycling. The Cycle Stop valve was the possible solution to that but that's out due to the pump power. The other solution would be to to add a whole lot of pressure tank storage (costly). This would also still be subject to wider pressure fluctuations.

    Pros: some water would be available in the event of a power outage, more water storage.

    Cons: much higher initial and operating cost, wire size would need to be 8 awg, space for pressure tanks, more difficult to adjust and maintain.

    With the constant pressure pump, if the literature is to be believed, my fuctuation should be between 1.5 psi to around 10 psi.

    Pros: steady pressure, ease of maintenance, operation and adjustment, cost, cheaper to run, only requires 10 awg wire.

    Cons: So far all I can see is instant loss of water with power outage - mitigated with a backup generator I already own.

    Can anyone shoot any holes in my thought process here other than I'm nuts to think it will work?

    Thanks again,

  12. John_NC

    John_NC New Member

    Dec 16, 2006
    Good idea to repost in well & pump forum.

    I'll ask the moderator if he can cross-post this thread to that forum.
    Last edited: Dec 17, 2006
  13. Master Plumber Mark

    Master Plumber Mark Master Plumber

    Feb 6, 2005
    Sensitivity trainer.. plumber of mens souls
    indianapolis indiana - land of the free, home of
    have fun

    Just filling up that whirlpool tub and trying
    to do laundry on the second floor at
    a constant pressure of 70psi will be interesting

    good luck..... happy plumbing
  14. vaplumber

    vaplumber Guest

    Youve got a static level of 35 ft, and water in well of about 500 gallon with 3.5 gpm recovery. Thats fine for now, but what about when the weather is hot and dry? Then you may have half the water level in that well, at only 250 gallon of reserve, and your recovery rate could be cut way down, and below what even one single fixture would flow. For large storage tanks, I have to question that. Even if you had several 120 gallon pressure tanks, once they are empty, that water to refill them has to come from some where. I would feed the well into a large cistern type tank with a low gpm pump in the well, then feed the house from the cistern via jet pump. 3.5 gpm may work on paper, and may even be fine as long as the ground water levels stay the same, but in the real world you wont be happy at all.
  15. John_NC

    John_NC New Member

    Dec 16, 2006
    Well production @ 3.5 gpm

    I hear you. I have hopes that 3.5 is already on the low end. The well was drilled during a drought year. (Water restrictions were in place for all public supplied residents). If I run out of water, I'll have to either drill another well or install a cistern as you say.

    Also, in this area, wells over 200' deep are relatively unaffected by dry conditions (so I'm told).

    All I can really do at this point is be optomistic and hope for the best with what I have to go on today. Speculating that I might have problems down the road and engineering a solution to that would be premature at this point I think.

    One thing that gives me hope is a friend of mine had a 250' deep well with only 1.5 gpm and he never had any problems even with (and I have no idea how he got away unscathed) a 6 zone sprinkler irrigation system he installed to water his 1 acre lawn.

    Also, my neighbor has a 100' well that produces 10gpm and has never experienced any problems even at that depth. I just got unlucky with my selection of my well site and missed any decent water vein.

    Wish me luck!
    Last edited: Dec 17, 2006
  16. Rancher

    Rancher Guest

    OK 3.5 gpm is literally nothing, you need an above ground storage tank to pump the water out of the well into, and then another pump to pressurize your water for you house, that way you don't have to count on your well providing the flow you need regardless of what your static water is. Oh by the way your static water is determined by no water use, if you use the water, then you static water may drop to 200-300. Back to the 3.5 GPM, FHA and VA loans require a well with a min of 4 GPM, so yours is below the minimum for a small trailer home... let along 6 bathrooms. I drilled a well that produced 19 GPM but that was a wet season, during the drought it drops to 2-3 GPM.

    You need a storage tank (Cistern).

  17. Master Plumber Mark

    Master Plumber Mark Master Plumber

    Feb 6, 2005
    Sensitivity trainer.. plumber of mens souls
    indianapolis indiana - land of the free, home of
    Cistern or a swimming pool

    I am sure that they make something that would work....

    one pump to pump it into the 5,000 gallon cistern,

    and then a shallow well jet pump inside the home to

    go into the large commercial bladder tank set at 70psi...

    of course, you could always try drilling another well
    somewhere on the property....

    are you sure that is spelled cistern, I thought it was spelled Systern??

  18. John_NC

    John_NC New Member

    Dec 16, 2006
    What part of the country is that Rancher?

    It sounds like you might be in a pretty arrid part of the country. It's pretty common to get 1.5-3 gpm wells around here (Central NC) My neighbor has a 5k sq foot house and is doing fine on 3 gpm for the last 6 years since he built. Also my friend I mentioned earlier had a 1.5 gpm well for the house he lived in for 6 years that he recently sold, no problem. Before I panic, I will check into the FHA / VA requirement. Do you know if that's across all states/areas?


    Last edited: Dec 17, 2006
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