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Thread: recirculation system issues....Too much of a good thing

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    DIY Junior Member bikeythekid's Avatar
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    Default recirculation system issues....Too much of a good thing

    Hello all-

    I have just finished (well almost finished) a renovation of a 6 story single family townhouse. The house is 16feet by 62 feet. Two recirculation loops were installed for the front and rear of the house controlled by a Grundfos timer. The plumber installed the hot cold and recirc. lines very close to each other and as a result the cold line warms up overnight (or anytime the water is not in use for 4-6 hours). I have cut open the walls and insulated the pipes but that didn't do much. I have not set the timer so the recirculator is currently on full time.

    If I don't know the future owner of the building (single family), what is a safe way to set the timer so as to reduce the warming and save energy? I was thinking of shutting it down from 12-5 am when instant hot water demand would be minimal. The top three floors are the bedrooms so the only hot water demand at that point is showers, baths and faucets. Do you think it is okay to shut the recirculation system off in the middle of the day when people are at work and school and the demand for hot water would be shifted to the kitchen and laundry (both are close to boiler room)? would intermittent on/off cycles help with the warming? Obviously, whoever moves in could change the settings. currently the house is unoccupied so there is a zero demand for hot or cold water. With 5-8 people living there with their water demands, am I right to assume that the warming won't be as much as a problem? If anyone can offer me a sample of how they have set recirculation system timers, that would be a great help.

    Secondly, How important is having cold water first thing in the morning vs tepid water? (3-4 min of warm water if no water has run or toilet been flushed through the night). The way I see it, you can brush your teeth with warm water (although the branch line gives 20secs of cold) but showering with cold is no fun. would you rather wait for hot water or cold water?

    I'm not against installing another cold line away from hot water lines but most people I speak with tell me that immediate hot water is worth a little tepid water in the morning (my wife and sister even claim to prefer it for morning face washing but I think they are just sick and tired of hearing me talk about it).

    I am interested in anyone's opinion on the matter and any advice on timer settings as well.

    Thank you,
    Bikey The Kid

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    Moderator & Master Plumber hj's Avatar
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    I find it hard to imagine that the pipes are so close together that the cold water would heat up, especially if they are insulated. If it were I, I would be doing some investigating to see if that is the actual problem. Additionally, all you need is enough circulation to keep the water hot, which is the purpose of modulating valves at the pump to reduce the velocity of the water.
    Licensed residential and commercial plumber

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    Quote Originally Posted by hj View Post
    I find it hard to imagine that the pipes are so close together that the cold water would heat up, especially if they are insulated. If it were I, I would be doing some investigating to see if that is the actual problem. Additionally, all you need is enough circulation to keep the water hot, which is the purpose of modulating valves at the pump to reduce the velocity of the water.
    What type valves do you use to modulate?

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    DIY Junior Member bikeythekid's Avatar
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    I've checked every thermostatic shower body, installed check valves on the pipes of every thermo. shower body but one, doubled up check valves near the hw tank as well as added one of those tanks that catches the overflow from too much pressure and insulated plus a 3 foot thermo loop. I turned off the recirculation system last night and will report the results. I have been so convinced it was a cross connection or something but the results were similar when I shut off the water floor by floor. I shut off the cold line in the entire house, kept a cold tap on in the basement,put a bucket underneath, next morning, not a drop.

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    Moderator & Master Plumber hj's Avatar
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    To test for a cross connection, you turn off the water supply to the water heater and then open a hot water faucet. If it is shut off there is no cross connection. The modulating valve is a valve, preferably a globe valve but any will do, between the outlet of the pump and the connection to the heater. You close it as much as necessary to just maintain the temperature in the hot water piping. You have spent a lot of time and money without first determining the actual problem.
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    DIY Senior Member Smooky's Avatar
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    When you install a recirculation pump in the hot water line there should be a separate line that goes back to the cold inlet on the hot water heater. With existing plumbing, there are valves that are installed under a sink and the hot water is sent back to the hot water heater in the cold water line. I this case you will have instant hot water but you will have to run the cold a while to fush the hot water out. Also even if there is a separate line to send the hot water back to the hot water heater it can get into the cold line if it is not done correctly. Proper placement of spring checks is important in this type of system. A pump in a loop causes positive pressure in front of the pump and negative pressure behind the pump. Water takes the path of least resistance so it will try to suck cold water into the system behind the pump and push hot water into the cold in front of the pump.

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    DIY Junior Member bikeythekid's Avatar
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    Interesting... I'm not sure the plumber put check valves on the recirculation system at all. We do have spring check valves at the cold supply line as well as an expansion tank and thermal loop. Wouldn't that stop any cross connection into the cold line? There's no doubt there is pressure building. Its a 120 gallon indirect fired tank with the hydronic heat running full time (outer tank) and no demand for hot water but the recirculation system constanly on. But wouldn't that pressure kick off the relief valve in the tank? It is a 40 foot run withh the hot and cold less than an inch away for most of the run. The contractor and plumber are willing to run a new cold line and join it closer to the bedrooms. At least that way the warmed water would supply the boiler as it runs down the building. I doubt we can find the space w/o being really invasive. My family is no longer moving in or I'd just leave it the way it is.

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    Quote Originally Posted by hj View Post
    To test for a cross connection, you turn off the water supply to the water heater and then open a hot water faucet. If it is shut off there is no cross connection. The modulating valve is a valve, preferably a globe valve but any will do, between the outlet of the pump and the connection to the heater. You close it as much as necessary to just maintain the temperature in the hot water piping. You have spent a lot of time and money without first determining the actual problem.
    If you must slow down the water(modulate) I would say the pumps running too fast. Size the pump properly and leave the valve full open.

    Also in this situation I would turn the cold water off to the water heater and leave the hot side pressurized and the circulation pump running.

    Now with the hot side still pressurized,turn off the cold water to the whole house and open a cold faucet and drain the pressure off the cold. This allows you to check for a cross connection when the circ pumps running.

    If you do it your way.......you cant leave the circ pump running.
    Last edited by Hackney plumbing; 02-04-2012 at 08:10 AM.

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