Where to connect hot water recirculation line at water heater?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by gplumb, Feb 4, 2007.

  1. gplumb

    gplumb New Member

    Messages:
    32
    Location:
    North Carolina
    I am installing a hot water recirculation system with a dedicated return line and a circulation pump at the water heater. There are two options for connecting the return line - the bottom of the water heater tank at the drain or to the cold water inlet at the top. I realize that unscrewing the drain hose bib can be a problem if it doesn't come out easily,i.e., it's only plastic and can break. If the connection is to the inlet, then an additional check valve is needed to prevent recirculation line hot water from feeding the cold lines when there is cold water demand in the house. What are the trade-offs?:)
  2. its better on top

    I think its better on top because the dip tube will
    circulate and stratify the returning water equally throughout
    the middle of the tank instead of being put back in at
    the very bottom....

    comming in at the bottom of the heater also gives the
    heater a false reading and probably makes it turn on more often...
    (that is my theory)


    either way you still need a check valve on the incomming coldline...
  3. GoTanklessToday

    GoTanklessToday In the Trades

    Messages:
    89
    Location:
    Renton, WA

    Concur.

    Make sure you install a boiler drain before it enters the heater to purge the air. We go shutoff, pump, boiler drain, shutoff, into tank.
  4. srdenny

    srdenny Plumbing Contractor

    Messages:
    361
    Location:
    SF Peninsula
    "comming in at the bottom of the heater also gives the
    heater a false reading and probably makes it turn on more often..."
    If the return line is properly insulated, the ∆T will not be so great as to confuse the thermostat. Plus, sending it back into the bottom of the tank stirs the water at the tanks bottom and helps prevent sediment buildup down by the burner...
    and that's my theory.
  5. GoTanklessToday

    GoTanklessToday In the Trades

    Messages:
    89
    Location:
    Renton, WA

    I wouldn't say that either way is the right way, I've seen it done both ways equally. The reason we would prefer it to go down the dip tube is that if its done right, you don't have to do any re-work when the heater is replaced in the future. Also, removing the drain valve and altering the "as manufactured" configuration, you are technically decertifying the UL or AGA rating. This "technically" voids the warranty.

    If I lived in a hard water area, I may consider the drain valve way more for the reasons you mentioned though. Keep the "junk" in suspension and allow it to flush easier.
  6. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,296
    Location:
    Yakima WA
  7. Randyj

    Randyj Master Plumber

    Messages:
    1,047
    Location:
    Alabama
    My 2 cents... I didn't read the other replies... but, logic tells me not to break any seals on the water heater and don't mess with it if not necessary. If you messed up threads or broke something then you've got the possibility of having to replace a water heater ... put that puppy in the cold side and do your gambling in the gambling houses.....
  8. harleysilo

    harleysilo New Member

    Messages:
    101
    Location:
    Georgia
    I recently installed a recirc pump, the type that mounts directly on top of the water heater. I am 75% satisfied with this solution. Even with it running for 15 min. on 15 min. off I still only have warm water immediately and have to weight 30 plus seconds for HOT water, 50 ft. run total. I too will be adding a dedicated return line and have been wondering the same question.

    After reading what's been posted here, and researching some I too agree plumbing it to the cold water side is the best and most logical solution.

    Less work when It's time to replace water heater and not risking running hose bib connection on bottom of heater are the prime reasons for me.
  9. gplumb

    gplumb New Member

    Messages:
    32
    Location:
    North Carolina

    I have looked into using the Laing method of connection, but they are the only pump manufacturer that specifies the use of the air vent near the pump (before pump if connecting to drain and after pump if connected to cold inlet). They also want the pump mounted below the top of the tank. They seem more concerned about air in the line damaging the pump then the the other pump manufacturers. Does anyone follow the advice about mounting their pump or other manufacturer's pumps below the tank top. Does anyone install the air vent (Watts FV-4M1)? To install an air scoop has to be built out of 1 1/4" pipe and a threaded fitiing put on it. My plumber said it would cost around $50 just to build the air scoop. :)
  10. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,296
    Location:
    Yakima WA
    Install your system according to the manufacturer's recommendations. My point in posting the link to Laing was to illustrate the two places where the connection to the tank can be made and was not to imply that you should install another brand of pump using the Laing instructions.
  11. srdenny

    srdenny Plumbing Contractor

    Messages:
    361
    Location:
    SF Peninsula
    When hooking up a return to the cold side on a wh near to and below a sink or lavy I've had customers complain that they were getting tepid to hot water out of the cold tap. The easiest way to prevent this is to put a check valve on the cold side immediately upstream of the return connection, which then requires the installation of an expansion tank. This would not occur if the return were piped to the bottom of the tank.
  12. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,296
    Location:
    Yakima WA
    Actual you do get warmish water from the cold even when going into the bottom and with an expansion tank. It's not really hot water, but luke warm. The expansion tank does its job in absorbing the pressure rise when the water is heating, but a certain amount goes into the sink faucet.
  13. got_nailed

    got_nailed DIY Senior Member

    Messages:
    277
    Part way off the wall but you might need to think about where you put a check valve if your using your well presser tank for expiation on the hot water heater.


    PS no i can't spell
  14. dubldare

    dubldare Plumber/Gasfitter

    Messages:
    286
    Location:
    MN/ND

    News Flash, get out your pens and make a note.

    Water is lazy, (as are air, people, etc) it will take the easiest path.

    A check valve upstream of the expansion tank and water heater will prevent this. Also, a check valve on the inlet side of the circ pump will negate any coolish water from backfeeding when the pump is off.

    I prefer to pump into the bottom of the tank. Biggest reason why: that two-bitter of a drain valve on the wh. After installing the nipple and tee for the recirc line, put in a ball valve with a male hose adapter. A full-port drain will make flushing and future replacement a breeze.

    Also, make sure to valve each side of the circ pump.

    Pumping the recirc into the bottom of the tank will prevent any stacking/stratification that could occur. There are a few wh's (non-circulated AOSmith Cyclones) where I have had to install a short 'spin-around' pump to prevent stacking. Basically, pumping from the hot outlet to the cold inlet to increase reserve capacity.
  15. gplumb

    gplumb New Member

    Messages:
    32
    Location:
    North Carolina
    What do you mean by "stacking/stratification"? When the recirc return line is put into the cold water inlet at the top of the tank it feeds to the bottom by way of the dip tube. Why would this be any different than feeding the return warm water externally to the bottom of the tank by way of the drain connection point?
    :)
  16. dubldare

    dubldare Plumber/Gasfitter

    Messages:
    286
    Location:
    MN/ND
    Well, another benefit to tieing into the drain valve port is simplifying the inlet to the heater. When you think of what has to go on that line: check valve, shutoff, exp tank and maybe a union....makes me want to pipe to the drain, if only for the sake of the next poor sod who'll have to deal with it.


    Now, the stacking and stratification I was speaking of concerned a certain type of commercial wh. They are bottom-fed, high efficiency commercial units. Units without circ pumps have a tendency to stack---where layers of water of different temperatures exist within the tank. Kind of like when you've swam in a lake (if you have) the shallower water is warmer than the deeper portions. The pumps I've installed in those cases was to stir this up, so that the tank is closer to a uniform temp.

    But it makes no difference, besides what I've outlined above, to dump your recirc into the inlet of a top-fed heater. It is getting the water down to the bottom of the tank. I just find it better to keep the inlet piping clean, and get a better drain valve at the same time.
  17. Tom3052

    Tom3052 New Member

    Messages:
    1
    Location:
    Chicago, IL
    Water gets colder

    Hope this thread is still active. I just installed my return line to the bottom of the tank. I also put the pump (Watts 500800) in the return line because I didn't want to potentially limit the flow on the hot side. Water circulates fine but as I shower the water gets progressivly colder. I had assumed I was drawing cold water up through the return line, but I believe the pump has an internal check valve.
    #1. Is it possible the temperature at the top of the tank is being diluted that quickly?
    #2. Am I, in fact, drawing cold water backwards through the running pump?
    #3 What about plumbing the return line back to the top of the tank, not through the dip tube inlet, directly to the top.

    Thanks
    Tom
Similar Threads: Where connect
Forum Title Date
Plumbing Forum, Professional & DIY Advice, Tips & Where to connect lav in basement bathroom? May 4, 2013
Plumbing Forum, Professional & DIY Advice, Tips & Where to tap of to connect drain for laundry room Feb 12, 2008
Plumbing Forum, Professional & DIY Advice, Tips & Where should I cut and connect the Galvanized Pipe? Jul 16, 2007
Plumbing Forum, Professional & DIY Advice, Tips & Do I need a flexible copper fitting where these lines connect Oct 20, 2005
Plumbing Forum, Professional & DIY Advice, Tips & Boiler system for hydronic heat - where to put check valves? May 5, 2014

Share This Page