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Anyone installing this unit domestic how water preheat

bob eck
bob eck Member Posts: 930
Good morning
Anyone installing the following drain water heat recovery unit. Gets installed on the main waist water stack and you pipe potable water into it and then into the water heater in the house. They say it warms up the cold incoming water temp and thus the water heater can produce more hot water and can use less energy.

Does this work? How much does it raise the incoming water temp?

Anyone using anything else to raise water temp?


  • kcopp
    kcopp Member Posts: 4,305
    I have one in my home and I have installed a couple others. It depends on a few things at to how much it raises the temp incoming water and hot hot a shower you take. The other factor I wonder it long term how a film build up effects the heat transfer.
  • ratio
    ratio Member Posts: 3,545
    I've thought about those somewhat. I think you'd want it only in the grey water, or maybe even just the shower/bathtub drain. The kitchen sink (at least at my house) is cold as often as hot, and the commode is never going to see warm water.

    Maybe a VRF heat-recovery unit, although I don't know many tinners who'd want to do repairs on something attached to the stink pipe!

    HVACNUT Member Posts: 5,476
    That's interesting. We just took over a country club account, fairly new building with all water source heat pumps and no backup. Not a tree in site for 100 yards. The last cold snap, the 2nd floor couldn't get over 58 degrees. 2 large Viessmann boilers supplying domestic hot only. We're going to pipe in a flat plate HX to raise the incoming water temp for the GEO's.
  • hot_rod
    hot_rod Member Posts: 20,790
    The bang for the buck is fairly good on those compared to solar or other pre-heat means.

    I suppose even if it raised incoming to ambient would be a gain.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • bob eck
    bob eck Member Posts: 930
    Hot Rod I think these would work great when tankless gas water heaters are used especially in the north part of the country with cold incoming winter water temps.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,840
    I've got one. I tested it with a receiversump, a pre heat storage tank and pump because the wife likes to take a hot bath at night, and in order for this to work, it must be a parallel matched load. In other words, if the hot water is not flowing down the drain while you are using it, it doesn't recover much heat. Even with the parasitic cost of operation, I calculated a 50% recovery rate.

    I then piped it into the exhaust of my mod con boiler, and ran all incoming water through the DWHXer first, as a pre heat. Essentially, I had a SUPER condensing mod con system :smile: I kept having a recurring night mare of the DWHXer failing and leaking CO into my house, so I took it out and moved it to my house in the mountains, where I installed it in the main drain stack where it would be the most efficient. Interestingly, I saw no evidence of acidic corrosion inside the DWHXer when I pulled it off the boiler. Unwarranted worrying.

    Quite honestly, I do not understand why these things are not eligible for a 50% tax credit. In my 40+ years of field experience, I've not seen anything mechanical with as good a return on the investment that can reduce energy consumption for DHW heating by 50%. The Quebec province REQUIRES them in new construction installations...


    BTW, it is considered a double walled positive leak detection heat exchanger so it complies to pretty much all code requirements.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,141
    Hello, I put one in my place, but piped it only to the main shower, so cold is preheated. Fun part was, it needed less than five feet of pipe to install between the unit and shower, so installation was easy and heat loss from connected piping is minimal. At the time (12 years ago) they claimed it saved 60% of the otherwise lost heat. I think it's more like 50% as Mark says. That number depends on the length of the unit.

    Yours, Larry
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,644
    @Mark Eatherton I wonder what your mod/con efficiency was then! I'm guessing near 99%.

    I've toyed with building my own, and piped my grey water separate with a nice vertical drop for one of these. Never did it, but with a real world number of 50% savings, I think I may go for it now!
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    Mark Eatherton
  • the_donut
    the_donut Member Posts: 374
    I’d hate to be the plumber trying to run an auger through that when it clogs.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,644
    The waste water is just a straight copper pipe. It's the domestic side which is wrapped around it.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • the_donut
    the_donut Member Posts: 374
    edited February 2018
    I’ve seen sediment and rocks plug mixing valves in my neck of the woods in Indiana. I’d hate to go fishing for that in a small hx.
  • FranklinD
    FranklinD Member Posts: 399
    They’ve installed them in all of the newly-remodeled college dorm buildings here. Our incoming cold supply drops down to 35-40° in the winter so I can imagine that every extra degree of temp rise would help.

    I’ve got the perfect spot in my basement for such a thing, and that stack only serves the 2nd floor bathroom (tub/shower, toilet, vanity)...and I have a wife & twin girls that looove long showers. Hmmmm.......
    Ford Master Technician, "Tinkerer of Terror"
    Police & Fire Equipment Lead Mechanic, NW WI
    Lover of Old Homes & Gravity Hot Water Systems
  • Leonard
    Leonard Member Posts: 903
    edited February 2018
    I think showers are only real potential saving for me, everything else (sinks) is relatively cool. Two 5-10 minute showers per day. I'm tempted but I wonder how long break even is for NH assume no install cost. Fuel is pretty cheap VS, lot of $$ copper in there.

    Would think a clean out tee at lest on the supply side of drain would be good enough for cleaning fowling . Maybe a tee on exit too.