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Thread: Hot water recirculation loop size?

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    Water system engineer riverside67's Avatar
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    Default Hot water recirculation loop size?

    What size should a dedicated hot water recirculation loop line be to be effective?

    Does the size of this line add to the volume capability of the main hot water feed line?

    Does it need to be the same size as the main hot water feed line?

    Thanks

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    Plumbing Designer FloridaOrange's Avatar
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    1. That would depend on the size of the system and the length of the hot system.
    2. No, because it is the return to feed the water heater.
    3. No, but in some instances it can be.

    For a typical system a 1/2" recirc line does the job.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

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    Water system engineer riverside67's Avatar
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    The length of the hot water system would be about 100' from the heaters to the furthest faucet/bathroom and about 100' back, total ~ 200' return line I'm presuming. I'm planning on having an 1.5" hot and cold water main trunk line ran from the heaters to the furthest bathrooms since both will have high performance type showers.

    We will have a 2" feed line coming into the home from our well.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The pumps in the recirculation systems I've looked at are designed for 1/2" lines, so I don't think you'd gain any benefit of a larger return line. Make sure you insulate those supply lines very well, or you'll be wasting a huge amount of heat with them acting as big radiators.
    Jim DeBruycker
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    Water system engineer riverside67's Avatar
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    jadnashua,

    Won't the supply lines be ran underneath my slab?

    How are the copper lines properly insulated under a slab?

    You are speaking of just the hot water supply correct?

    Does the hot water return need to be insulated also?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    A very large hot water pipe in contact with the soil underneath the slab without insulation will waste a huge amount of energy. No easy way to tell if they are insulated now, but you might see something as it comes up through the slab. the lines could be anywhere in the house or attic.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Water system engineer riverside67's Avatar
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    My mistake...I forgot to mention that the house is not built yet. We are building it starting in April. I am just trying to make sure I have certain systems correct when we go to construction so I can correctly explain to my contractor what we want exactly. The hot water recirculation system is one of them.

    So I assume the new hot water lines will be installed under the slab and pop up into all wet wall locations (single story).

    Knowing this, how would the two hot water lines be insulated?
    Are hot water lines normally insulated in non-recirc systems?

    Thanks

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    Running supply (and drain) pipes under the slab happens a lot. No choice on the drain lines, but those can be plastic which is pretty inert and usually problem free. Not necessarily so with metal pipes. I'd prefer to run the pipes in the walls or ceiling. While a pain to repair, if it ever comes to that, much easier than trying to find a leak underground. Some soils are really bad on metal pipes. Plus, if your ground water table is high, the thermal load increases radically since the moisture will sap away the heat even faster. If you can design a utility room near the main points of use, I think you'd be much better off than running 100' of pipe.
    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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    Moderator & Master Plumber hj's Avatar
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    The cuculation line can be almost any size. I have even used 3/8" o.d. copper tubing, because all that is necessary is that flow be maintained. In fact larger sizes can produce more flow than is needed, but they are seldom valved down to slow the flow. 1/2" copper is usually used, but only because that is what we have lots of fittings for. Insulating hot water pipes is always beneficial, and here, ANY copper lines under the floor have to be insulated.

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    In the Trades Gary Swart's Avatar
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    I love my recirculating hot water set up, and I'm sure you will too. I would urge you to reconsider burying your copper water lines in concrete. Concrete tends to erode copper pipe and there is nothing more difficult to find and repair than a leak embed in concrete. We have frequent questions on this forum regarding this problem, and there isn't a simple, easy, or cheap fix. Although I am not a professional plumber, it is my opinion that burying copper pipes in concrete should be a code violation.

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    Water system engineer riverside67's Avatar
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    Since I'm neither a contractor or plumber I have no idea how the copper water lines are ran under a slab. What I do know is the lines are not "in"the concrete except for where the lines pop up thru the slab into the wetwall locations. I suppose the lines could be ran thru the attic but I'm not sure what California building code allows or prohibits.

    Would the insulation method be the same in both cases? If not, how would it differ between underground and attic installations?

    I will request 1/2" return line.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The issue with the ceiling is you have to be careful to ensure it doesn't freeze. In the summer, it can become quite hot. If they are run underneath the insulation next to the ceiling, that normally isn't a problem. Underground, the temperature is more consistent, but especially if you are in earthquake country, a break under there will be a major pain. Don't think that there's a code issue involved here. A big consideration is if you are in an area that gets below freezing, and stays there. If not, if placed under the insulation, you shouldn't have to worry about it.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Water system engineer riverside67's Avatar
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    jadnashua,
    Now that you mention the freezing aspect I remember that my fire sprinkler system will be required to have anti-freeze in it due to our elevation (4336). I believe this will prohibit the water lines from being up there. I'll discuss with the plumbing subcontractor.

    Any idea what is used to insulate copper pipes underground...would it be the thick black pipe wrap tape?

    Gary,
    I know in Ca it is plumbing code to have any copper coming thru the slab to be within a plastic sleeve so it does make direct contact with the concrete.

  14. #14
    Retired Defense Industry Engineer jadnashua's Avatar
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    I'd probably use the thickest foam insulation I could buy. I think that is around R-5 or so, but don't remember. These are a slit tube that gets sealed after installation. The pipe in the attic probably isn't an issue. If the house were to be vacant, you'd want to shut off and drain them. The sprinkler system, on the other hand, you'd want to still be hooked up, so to prevent freezing, I can see the antifreeze. I think I've read that sprinkler lines are dry until a head gets triggered on some systems.
    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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    Water system engineer riverside67's Avatar
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    Okay, sounds good.

    Let me ask this...I'm planning on using the Grundfos UP10-16BU ATLC recirculation pump with 1.25" union fittings but I wanted to have an 1.5" supply line ran from the two heaters, in the garage, to the furthest bathrooms.

    Will it be a problem to bush up to 1.5" after the pump?

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