Hot Water Recirculating System – Installation Tips

19 responses

  1. Kevin
    November 22, 2012

    Is there a recommended pipe size for the return line ? My supply line starts at 3/4" copper but does reduce down to 1/2" at the faucets so I was planning on using 1/2". Then I started thinking of the 50" coils of 3/8" or even plastic. Does it work best with copper ? Thanks.

    • Tim Carter
      January 6, 2013

      Kevin, your question require lots of typing and I have some questions for you. You should consider investing in a 15-Minute Consult with me. Look at my cart for that. Lot's to discuss. I just do short pithy answers here.

  2. Robert Harris
    March 12, 2013

    If there is a power failure using a hot water recirculator pump (gas water heater), will hot water still be available as if there were no pump? (or will the pump and valve prevent flow?)

    • Tim Carter
      April 1, 2013

      Robert, Walter, this is what my 500-Second Consult is all about. Click the Shop icon at the top of the page!

      • Roger Swanson
        December 16, 2013

        I have a ranch with basement, insulated 3/4 inch copper tubing. Takes about 40 sec for hot water to arrive at bath. about a 20 ft run.
        Would Pex work for the return of a gravity water circulation? I would assume copper to heater drain. Typical 40 Gal gas water heater. Is drain 1/2 in or 3/4 male? can see.
        Rog Swanson

      • Tim Carter
        December 31, 2013

        Pex should work. I've not tried it. The key is the entire line except for the last feet returning to the heater MUST be insulated. Read ALL of my columns about hot water recirculating loops. There are several!

  3. Ava Cocchi
    August 13, 2013

    I hope someone can help. Our plumber did a recirculating system but attached the hot and cold pipes together throughout the house so when our hot water runs it gets cold first and the reverese for our cold water. Also our toilets always have hot water running from them. Our gas bill was so high the gas company thought we had a gas leak and it seems that our hot water heater is running alot causing the meter to spin. HELP

  4. joe
    March 16, 2014

    Hi my question is if the reciculating pump comes with a check valve in it . do i need to put another one in the cold water supply line?

    • Tim Carter
      March 16, 2014

      Usually no.

  5. Frank Czubala
    August 19, 2014

    I have a 75 gallon water heater that I just changed out last week. I also have a 1/2" gravity recirculation pipe that was installed by the builder. My question is that I am not getting hot water at the furthest fixtures for over a minute where I did before the new heater? There is a check just off the tank drain and a ball valve right above it. Not knowing how it was installed could it be air locked? If so will it correct itself at some point? Thanks

  6. Roger beck
    January 5, 2015

    Your comment on shutoff valve above the water heater. If the criteria in you senario is the same except you do not put any shutoff valves above the water heater, won't you have the same explosion? If not, where is the pressure relieved?

    • Tim Carter
      January 7, 2015

      Easy. The pressure is relieved at any of the faucets in the house. Believe me, they'll start to drip when the pressure gets high.

  7. Marion
    March 7, 2015

    I have been looking for this, so thank you. I need this for 2 heaters, the gas hot water,because I am on tank water and for the combustion wood heater,which ideally I would like to use with a water jacket behind it as a floor heater to use less wood or even for a hot water supply. Can this be done?

  8. haydn
    May 23, 2015

    Hi Tim, I liked your little explain on hot water systems. Gravity circulation designs are a simple pump free idea in use many years ago when hot water systems were open vented. On these designs the check valve of choice is a swing check valve installed horozontaly, a) stops water being pulled from the base of storage unit and b) importantly adds very little resistance to the convection flow of the water. Regards.

  9. Peter Jacobson
    June 25, 2015


    We have a 75 gal gas hot water heater with a circulating pump that returns below the drain valve. So what do I do to drain the hot water tank to get the sediment out, without draining all the hot water out of the rest of the house through the loop return?



  10. Dan
    March 21, 2016

    Hey Tim, my house was pre-plumbed for circulation; when I recently changed the heater (it was previously feeding both ends of the hot water loop), I decided to add a recirc pump. I placed the pump at the end of the loop, right before return to the drain tap of the heater. Works fine, BUT, the pump seems to be injecting air into the system. I have NO leaks; to isolate, I just turn pump off, bleed out all air. Is fine until I turn pump back on; a short time later I have air in the system. I have run this isolation step multiple times; air IS getting in when pump is on, no water is leaking from any joint. Have you seen this before?

  11. Brent Olsen
    May 4, 2016

    so after 3 years I finally got around to installing a pump on my return line. added it to the bathroom central fan circuit (with a relay) so that it runs when the fan is turned on. Everything works awesome just one problem: the water runs yellow for the first 10 seconds. What could possibly cause this in the return line over 3 years?

  12. Larry B. Houck
    June 10, 2016

    I need some advice on how to correct a problem with a hot water recirculating line.We just had a new hot water heater just like the old one and we have had a hot water recirculating line for years with the old hot water heater which worked like a charm. It has a check valve installed but after some local plumber changed out the old hot water and installed the new one and reconnected the existing hot water recirculating line it will not work properly. I have had the plumbers back twice already and they purged air from the hot water recirculating line and it still will work like it did before. Do you think the line may still have air in it or could it be another problem?

  13. F, Dan Walker
    September 14, 2016


    I feel complied to as why don't you show a 'diagram' to aid those thof us that can not visualize what you are providing. For some, such as myself, instructions provided are really helpful, BUT a diagram would add so much in understanding.

    PS What happened to the 'FIRE PIT'? I truly enjoyed reading that.

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