New house: Question about long lag until hot water and use of circulator

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by breece, Sep 13, 2008.

  1. breece

    breece New Member

    Messages:
    3
    Hi, searched for this topic but didn't find anything that quite addressed it.

    We have a brand new house built within the last year. It is approx. 3900 sq feet (2 stories) and was equipped with a hot water circulator. We have a gas water heater with a 75 gallon tank. The water thermostat is set at the "A" setting (approx. 130 degrees F).

    When the circulator is off, it takes approximately 6 minutes (I have timed it) for the water to become hot in the kitchen sink. The kitchen is quite close to the garage where the tank is located.

    With the circulator on, the water is hot within seconds.

    So, what's the problem you may ask?

    Question 1) Regardless of the circulator, does the 6 minute hot water latency suggest there are any problems with our plumbing?

    Question 2) Are there any issues with leaving the hot water circulator on all the time? I have the circulator on a timer, but I find that even leaving the circulator off for 45 minutes will prevent us from getting hot water relatively quickly (within a few minutes). The builder told me we should avoid using the circulator since it is very hard on the pipes, but then backtracked when he saw how long it took us to get hot water with the circulator off. I am a little concerned about the energy costs and potential wear and tear on pipes from leaving the circulator on all the time and want to ensure that the circulator is not compensating for/masking an underlying problem with our plumbing.

    Note, a new baby means that we temporarily need access to hot water even in the middle of the night. After the baby sleeps through the night, we'll at least be able to turn the circulator off while we sleep.

    Thanks for your answers and insight.
  2. Gary Swart

    Gary Swart In the Trades

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    7,328
    Location:
    Yakima WA
    I can't help much on the time lag although 6 minutes does seem to be a very long time. As far as the recirculating system is concerned, I can just relate my own experience. I have been using a recirculating system for about 4 years and I never turn the pump off. I'm sure there is more wear on the pump doing this, but I figure that the added wear plus the small increase in electricity is just the price of have instant hot water anytime day or night. I have no clue as to how much the electricity costs per month to run that small motor, but it can be much. I will have to admit that I don't have anywhere near the size house you have, and perhaps that will make some difference although I don't really see how it would cost more to operate. Be sure you insulate the hot water pipes both on the supply side and the return line.

    I'll be watch this thread to see what opinions the pros offer on the time lag without the recirculating pump.
  3. maintenanceguy

    maintenanceguy In the Trades

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    107
    Location:
    Pennsylvania
    6 minutes seems like a long time but that's why the architect added a circulator. Run the circulator if you want instant hot water.

    Your builder is right, hot water circulator loop piping wears out faster than piping without a circulator. I see it in commercial buildings all the time. But it's a difference of springing leaks in 25 or 30 years instead copper pipe lasting 35 or 40 years.

    Not that big of a difference. I'd run the circulator.
  4. hj

    hj Moderator & Master Plumber Staff Member

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    26,472
    Location:
    Cave Creek, Arizona
    water

    When the circulator is off you have to flush the ambient temperature water out of the pipe, AND heat the pipe up. Doing both of these tasks is why it takes 6 minutes. The circulator does them constantly so you get water immediately. Either run the circulator continually, but if it was installed properly there is a valve between the pump and the tank that you can shut off to the point where the water is just staying hot, but the velocity is not high enough to damage the piping, or reset the timer so the pump turns on periodically to maintain the temperature.
  5. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Two things could be causing the 6 minute delay: In your large house, they may have used larger pipes..maybe even 1" pipe....for the main runs. That means that much more water which has to be pushed out of the pipes. And, although your kitchen seems to be near the WH, the pipes may in fact run to the far end of the house and loop back to the kitchen.

    I don't see any solution except to run the circulator. We can hope that the plumber isulated all the hot pipes well, so your energy loss will be minimal.
  6. breece

    breece New Member

    Messages:
    3
    Thanks everyone, your perspective is helpful towards our peace of mind.

    I agree with maintenance guy and Gary Swart and am willing to have a moderate amount of additional wear and tear on the pipes for the wonderful benefit of speedy hot water. I'll just be sure to mark my calendar to sell the house in 24 years instead of 35!;)

    Oh, one other related question: We were experiencing a consistent knocking (water hammer?) in our master bathroom a few months after we moved in. This was a regular knock every 5-6 minutes or so throughout the day. It did not coincide with us running the hot water. We had the builder and their plumber over, but they couldn't diagnose the problem. At the time we were running the circulator continuously. Once I put the circulator on a timer, it seemed like the knock abated. In your experience, can running a circulator cause pipe knocking?

    Thanks all.
  7. breece

    breece New Member

    Messages:
    3
    HJ,

    Just wondering if I understand which valve you were referring to in your post that is between the circulator and the tank.

    Would I turn the valve in the image below?

    [​IMG]

    Regards.
  8. jimbo

    jimbo Plumber

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    8,997
    Location:
    San Diego
    What I don't see in your picture, but it may be there, is a thermal switch. This is a thermostat snapped on to a water pipe on the return side of the pump. When the return water is above that set point ( about 80 or 90º) the pump doesn't run. This set up improves the energy efficiency, and doesn't noticeably affect the hot availability. If you do not have one, it is a simple and inexpensive addition.
  9. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    No, that screw on the pump is part of the pump.

    1. Below the pump it looks like you have a checkvalve. (good)
    2. It looks like you have insulation on all the pipes. (good)
    3. It's timer based, but I also see a wire that might lead to a thermal switch.

    I also see you have a drain line connected to the T&P valve. (good)
  10. MrRedyTemp

    MrRedyTemp New Member

    Messages:
    12
    That center screw is used to manually rotate the pump head when it doesn't due to whatever reason after plugging it in. As for the noise from the pipes, since you say it stops when the circulator was placed in timer mode. A pressure regulator could be playing a part. Time the interval of the sounds to see if their consistent, use a stop watch or second hand on your watch. Then see if the circulator or other device is also operating / cycling at that same interval. Pipe hammering often doesn't happen in "moving water" but instead when water "stops" suddenly. Check out this page for info: http://www.factsfacts.com/MyHomeRepair/PipeNoises.htm Hard to zoom in enough to see the model of the pump. But you might find some answers here http://www.us.grundfos.com/web/down...tToCategory=HVAC#11.1&RestrictToCategory=HVAC

    Hot water circulation utilizes minimal electrical energy, but running hot water 24 / 7 through your pipes will take a big bite on your gas bill. At Temtrol DeltaT we've done some number crunching in the past and came to the conclusion that "If you limit your usage to two hours in the morning and two hours in the evening, your likely to not see an increase in your gas bill". This is due to the waste of waiting for hot water is cancelled out by the savings from not waiting for hot water after you've installed one. Anything beyond the 4 hours a day, you could see change in your bill. It's often hard to tell if all your hot water pipes are insulated to be efficient. But, it should be faiirly easy to tell if they really are by timing how long the water in the pipes does stay hot / how quickly it gets cold. This test is of greater importance to homeowners who wait for hot water in their kitchens since your dishwasher can use a great amount of electricity to heat the water needed for the dishwater to do it's job...everytime you use the dishwasher adds up over a year.

    I notice that your using a tank water heater, but our upcoming tankless model would work to really move the water "when needed". We plan to release a Tankless Hot Water Circulator Recirculator October 1st of this year. It has a push-button single cycle operation as well as the timer control mode, occupancy sensored capabilities, etc. Unlike others on the market, the RedyTemp Tankless model has adjustable temperature control to allow you to choose your optimizal comfort temp. Anyhow, hope this has been of some help.
  11. camner

    camner New Member

    Messages:
    5
    Does anyone know if RedyTemp has released a pump for use with a tankless system (and for a house without a recirculation line)?

    How would such a system work? Where does the pump "push" the water when there is no tank into which to push it?
  12. leejosepho

    leejosepho DIY scratch-pad engineer

    I believe this is important for protecting the insides of lines, and I hope it does not get missed.
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,888
    Location:
    New England
    Other than the fact that a tankless system often needs special setup to last when using recirculation, you shouldn't need a special pump to do it on any system. The RedyTemp unit has an internal valve that opens to connect the hot to the cold when it is running. Other than the fact this is in the self-contained box, it is the same concept as any other recirculation system - at some point, normally the furthest fixture from the WH, you have to install a crossover valve to allow it to circulate the water. You can eliminate the valve if you have a dedicated return line, but all of them require a check valve. What sets the RedyTemp apart from the others is the easily adjustable thermostat and the fact that it is entirely self-contained at the point of installation. Assuming you have power available, it takes all of about 5-minutes to install one. I have mine to stop when the temp is warm, rather than hot. This give hot at the closer fixtures, (the inlet to the shower is closer so it is hot before the sink) and means not that much warm gets pushed into the cold line.

    The thing that may give people trouble understanding is the difference in pressure between the hot and cold lines is essentially zero, and if you connect them together, it is easy to move the water from the hot side to the cold side. If you follow the cold water back to where it comes from, you'll find it is feeding the WH, whether a tank type or tankless. So, when recirculating using a cold line as the return, you push cold backwards with that from the hot line and it eventually ends up supplying the WH with hot on that side if it runs long enough. That presents the biggest disadvantage to using a recirculation system without a dedicated return line - the cold supply line will end up getting at least warm to a point. The design of the Redi-Temp unit limits that, especially if you don't require max hot at the box. The disadvantage to that unit is the pump on/off cycles mean it probably won't last as long as one where the pump runs all of the time. They claim the checkvalve should last at least a million cycles, but the pump certainly won't. Mine's going on 5-years and still works as new, though.
  14. hj

    hj Moderator & Master Plumber Staff Member

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    26,472
    Location:
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    valve

    The screw in the middle of the pump is a cover for the motor shaft. The water flow control valves are the devices with a slot in them on both sides of the pump in the flanges.
  15. leejosepho

    leejosepho DIY scratch-pad engineer

    Do you recall whether the article mentioned anything about a check valve? Without one, I believe the recirc line could run backwards and deliver tepid water to the faucet. I have a swing-check valve in my own pumped recirc line to be sure that does not happen.
  16. xroad

    xroad New Member

    Messages:
    113

    I do not recall mention of a check valve in the article, it was a long time ago. I did a search on the word "gravity" here and found another thread on this topic. A check valve was mentioned. Cannot use a spring loaded check valve, has to be a flap type. Alos talked about drilling a small hole in the flap ..... I got lost after that.

    My problem is that the last 7 feet of the pipe run at the far end is in a very cold unheated underside of an enclosed porch with minimal insulation and plenty of air leak. I don't know if the gravity system will work. I suppose the downward force of the return water have to overcome any downward force in the supply pipe. In my case, the supply pipe water will get colder and colder as it move toward the far end. At what point, when the water gets cold enough, will it exert a backward force IN THE SUPPLY PIPE? Will this force be overcome by the force in the return pipe? A check valve may prevent backward flow but it won't help if the water don't move either.
  17. xroad

    xroad New Member

    Messages:
    113
    Just thought of something. It SHOULD work. Even though the far end, last 7 feet or so is in a cold environment, both the supply and the return pipe is in the same environment. So they will have equal forces on that section and they SHOULD cancel out. The temperature differential at the rest of the pipes will drive the passive circulation. Make sense?
  18. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,888
    Location:
    New England
    Running hot water lines through an unheated area, then adding recirculation will add a lot of cost to the operation. You really need to insulate both the supply and return lines.
  19. leejosepho

    leejosepho DIY scratch-pad engineer

    I would say that is likely, but I do not know for sure.

    I used to live in a large and poorly-insulated house with a large coal furnace that had been converted to gas but was still dependent upon convection (no forced air). The gas bill there was atrocious, but the house did stay sufficiently warm ... and my point here is this: Natural convection or "gravity flow", at least as I know it, for anything related to heating is far from efficient. So yes, your line might stay warm that way, but you will likely need a circulation pump if you want truly-hot water quickly available at the tap.
  20. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,472
    Location:
    Cave Creek, Arizona
    circulation

    Gravity circulation will work great, UNTIL the first place the pipes turn downward, such as a jog under a beam in a basement, or going into the concrete floor. A gravity system either has to be designed for it, OR the installer has to have a lot of luck so it happens accidentally.
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