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Metlund D’Mand hot water recirculation pump

Rian Bart | Posted in Green Products and Materials on

I am thinking about installing hot water recirculation pump to reduce hot water usage. Metlund D’Mand hot water recirculation pump seems to be a good choice since it’s passive and does not use energy until you push a button when hot water is needed.

I spoke with a contractor and he is against recirculation pump since he has seen multiple cases of pipe bursts probably due to the turbulence and pressure created by the recirculation pump. I did some web search and found some horrible stories also such as http://www.amazon.com/Laing-ACT-303-BTRW-AutoCirc-Retro-Fit-Circulator/product-reviews/B001U66R7S/ref=cm_cr_pr_hist_1?ie=UTF8&showViewpoints=0&filterBy=addOneStar ,

What’s your opinion on hot water recirculation pump? We use copper pipes in CA. I don’t want to place a water bursting time bomb while trying to save some hot water.

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Replies

  1. Brent Eubanks | | #1

    We have one of the Metlund D'Mand units, and have used it for years without a problem.

    I've never heard of pipe bursting being attributed to pumps of this sort (and a quick google search didn't reveal anything). At any rate, turbulence does not burst pipes -- pressure does. But pressure could only build up if there is a blockage in the pipe.

    Note that the Amazon review you link to specifically said the failure was not in the pipe, but in the pump housing itself. I know nothing about the product they're discussing (made by Laing), but I can say that the Metlund product uses an all-metal housing and a good quality pump. Short of an actual manufacturing defect in the product, or freezing, I can't imagine it bursting.

  2. Expert Member
    Carl Seville | | #2

    I've used D'mand pumps on projects for many years with no problem. I have never heard of them causing pipes to burst. The primary benefit with this type of pump is that is doesn't circulate water after it is delivered to the fixture, saving a significant amount of energy over full time or timer operated pumps. It is also the only type of pump that works with tankless heaters. The only problem I have run across was once I installed one with a tankless heater with a 1/2 return line with lots of elbows in it. The return line created too much resistance so the pump wasn't able to pull a high enough volume of water through the pipes to turn the heater on as the heater needed a minimum flow of water to begin operation. Relocating the pump to where I could jump it between two 3/4" lines solved the problem.

  3. Riversong | | #3

    The potential problem with recirculating systems is with constant circulation, which can increase erosion corrosion, particularly with hot water, hard water, and acidic water. Copper piping gets quickly coated on the inside with insoluble calcium carbonate which protects the pipe from further corrosion and erosion, except with excessive water velocity and excessive turbulence - caused by too small a pipe, inadequate deburring, poorly-fitted connections, too many 90° angle changes, excessive flux or excessive solder.

    From the Copper Tube Handbook:

    To avoid excessive system noise and the possibility of erosion-corrosion, the designer should not exceed flow velocities of 8 feet per second for cold water and 5 feet per second in hot water up to approximately 140°F. In systems where water temperatures routinely exceed 140°F, lower flow velocities such as 2 to 3 feet per second should not be exceeded. In addition, where 1/2-inch and smaller tube sizes are used, to guard against localized high velocity turbulence due to possibly faulty workmanship (e.g. tube ends which were not properly reamed/deburred) or unusually numerous, abrupt changes in flow direction, lower velocities should be considered.

    Locally aggressive water conditions can combine with these two considerations to cause erosion/corrosion if system velocities are too high.

    Due to constant circulation and elevated water temperatures, particular attention should be paid to water velocities in circulating hot water systems. Both the supply and return piping should be sized such that the maximum velocity does not exceed the above recommendations. Care should be taken to ensure that the circulating pump is not oversized, and that the return piping is not undersized, both common occurrences in installed piping systems.

  4. Brent Eubanks | | #4

    Robert,

    Are the problems you are describing realistic issues for a system that only operates periodically (as with the D'mand system)? Continuous recirculating systems could certainly cause erosion, but I'm having a hard time believing that the sort of wear you describe could happen significantly from just a few minutes of operation per day.

  5. Riversong | | #5

    Brent,

    The first sentence in my last post said "constant circulation". I doubt you'd have any such problems with demand circulation, though you won't get the efficiency improvement unless your pipes ARE sized small enough to move the hot water quickly to the fixture, which means that parallel piping systems are preferred over branched systems, and small-diameter low-turbulence insulative PEX systems preferred over copper systems.

  6. Anonymous | | #6

    We had a pipe burst in our house due to a recirculating pump. I wish someone had warned us about this years ago. This has been a very expensive lesson.

  7. Riversong | | #7

    Yet another example of the "revenge effects" or unintended consequences of technological "solutions" to technological problems.

    Check out the book "Why Things Bite Back: Technology and the Revenge of Unintended Consequences" by Edward Tenner: http://www.edwardtenner.com/work2.htm

  8. Anonymous | | #8

    Metlund D'MAND pumps cannot cause a pipe to burst. The pump is a delivery system for hot water and it supplies hot water to every fixture between the pump and the boiler once activated. The Metlund pump is actually the only pump that delivers a return on investment because it saves on energy (between 8,000 and 12,000 gallons of reduced water going down the drain a year ((sewage costs and water savings)). The Metlund pumps life span is much longer than other recirc pumps because hot water never goes through the pump, which is the leading source of recirc pump corrosion.

  9. Riversong | | #9

    Yet another anonymous sales person hyping their wares.

    We really gotta stop this back-door advertising. No more anonymous posts!

  10. Keith Murray | | #10

    is a back-check valve require to keep the hot water circulating system from pumping back to the utiltiy's main?

  11. Aj Builder, Upstate NY Zone 6a | | #11

    Keith, the pump circulates water in a loop back to hot water source cold intake and NO it does not send water back to cold water source like your well or back to the street. The kits come with directions and you can view directions ahead of time for almost anything by looking for the PDF at a manufacturers website.

  12. Craig Crickard | | #12

    In general on-demand systems are safe and economical. Taco also makes a D'Mand Recirculator System that is well-regarded.

    http://www.pumpproducts.com/taco-554-plumbing-kit-for-006-008-39-mand-system-p-17978.html

    These units are easy retrofits that require no new piping. They have a low annual operating cost ( about $1 per year) and a life expectancy of 15-20 years so they quickly pay for themselves. They cut down on the electricity used in continuous hot-water circulation and nix the tendency to turn the hot water on and walk away while waiting for the temperature to rise. By circulating water that is at the ambient temperature of the house back to the hot-water tank they use less energy than chilled water and by moving water more quickly than the fixture flow rate, there is less heat loss in the piping en route to the fixture. The D'Mand systems are currently among the most sustainable home products on the market.

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