Hot water recirculation loop size?

Discussion in 'Water Heater Forum, Tanks' started by nofears67, Jan 18, 2010.

  1. nofears67

    nofears67 New Member

    Messages:
    186
    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
  2. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    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.
  3. nofears67

    nofears67 New Member

    Messages:
    186
    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.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    21,817
    Location:
    New England
    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.
  5. nofears67

    nofears67 New Member

    Messages:
    186
    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?
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    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.
  7. nofears67

    nofears67 New Member

    Messages:
    186
    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    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.
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,270
    Location:
    Cave Creek, Arizona
    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.
  10. Gary Swart

    Gary Swart In the Trades

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    7,308
    Location:
    Yakima WA
    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.
  11. nofears67

    nofears67 New Member

    Messages:
    186
    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.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    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.
  13. nofears67

    nofears67 New Member

    Messages:
    186
    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    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.
  15. nofears67

    nofears67 New Member

    Messages:
    186
    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?
  16. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    Doing it that way would restrict the overall flow and negate the larger supply pipes. Put the put in the return line where both the inlet and outlet are the 1/2". Often, they put a T on the drain of the WH and run the return line in there when you have a dedicated line for it. So, you'd take the 1/2" tap off the furthest point, run it back to the WH and run it into the bottom of the WH. The system would come with a check valve to prevent water going the other way.
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