Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

GFX plus ΔT Logic

Dave_4 Member Posts: 1,405
I believe ME was recirculating waste water. GFX star is recirculating potable water form a storage tank.


  • Uni R_2
    Uni R_2 Member Posts: 589
    The GFX-Star looks interesting...

    A GFX plus a small Taco ΔT-controlled circ makes an interesting combo.

  • Larry Weingarten
    Larry Weingarten Member Posts: 3,331

    Seem to remember that Mark Eatherton was working on a similar system. Keeping things from gunking up was a concern. I use a GFX on the cold supply to a shower. I know it's not the most energy efficient application, but it has the least to go wrong ;~)

    Yours, Larry
  • Uni R_2
    Uni R_2 Member Posts: 589
    With all due respect to ME...

    Take an existing passive product, graft on a smart circ and you potentially gain a lot of efficiency. Some of that new low wattage pumping tech that can't quite hit the North American mainstream market would really help.
  • ALH_4
    ALH_4 Member Posts: 1,790
    Confused and skeptical

    Call me dense, but I'm having a hard time understanding what the "DHR efficiency" is showing.

    Why not put a btu meter on the coil side and take a 10 minute shower at 2.5gpm? Then you know the input and you know the output and you can calculate at least some sort of meaningful efficiency.

    I have no experience with these units, but I have a feeling the heat recovery is relatively small in most residential applications. Adding a pump and another heat exchanger just decreases the heat transfer efficiency and adds a parasitic loss due to the pump motor.

    A btu meter would tell the story pretty quickly. I may be completely wrong, but why didn't they do this in the first place? Why don't they tell us the temperatures of the wastewater or cold water inlet? This setup would work much better when draining a 180°F bathtub with 40°F cold water inlet than a 100°F tub with 60°F cold water inlet.

    I am sure they transfer heat, but I have a feeling these numbers are overstated. This is reminding me of Ken's Law of Marketing. ;-)

    EDIT: I found temperature information indicating 42,500 btu/h transferred based on the Seattle information in this diagram. For a 10-minute shower that would be approx 7,000 btu, or about 8-10 cents per shower if coupled with a natural gas water heater. At 3 showers per day, that is approx $100 per year. Looks like between 3 and 7 years for the unit to pay for itself not including installation labor or other materials.
  • The Wire Nut
    The Wire Nut Member Posts: 422
    The GFX is nifty...

    ... if it's put in properly. IMO, the best application is a 5' GFX with a 2" pipe that uses shower waste water to heat the incoming cold water for the shower. Concurrent loads have the best potential... no circ, works, etc.

    But the walls have to be open, a vertical installation is required, and copper is pretty expensive right now.
    "Let me control you"

    Lost in SOHO NYC and Balmy Whites Valley PA
  • [Deleted User]
    I was circulating both....

    waste water and potable water. The addition of the pumps only squoze (BONUS points, new word for scrabble) an additional 10% out of the system as a whole. Hardly worth the effort.

    The biggest problem was controlling the odiferous output of the waste water tank. When it got warm in the basement (summer) I found myself dosing the tank with clorox 2 times per week. Not a big deal in the city, but it would spell biological disaster for an individual sewage disposal system (gubbernmint speak for septic tank and leaching field...)

    If I had to do it again, and I will be, I'll be doing as Constatin said and installing it only on the master shower.

    The heat exchangers are great, when properly applied. Attempting to add additional bells and whistles to it can only go so far.

  • Bob Gagnon plumbing and heating
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Bob Gagnon plumbing and heating
    Dual savings

    My greywater recycling system with heat recovery is working good. A slow dissolve chlorine tablet keeps the tank from smelling. I am recovering about 25% of the heat off my shower water and cutting my water usage by about half. I ran pex around the outside of a 150 gallon tank and dropped a large custom made tankless coil into the greywater tank. The PEX and coil each pickup about 10 to 15 degrees. My shower water drains out the bottom so the hot shower water is trapped in the greywater tank at the top. There are no moving parts or pumps except for the greywater pump. I feel we can collect more heat if we store the greywater in a tank, because the heat will migrate into the pex and copper coil most of the time. Plus we save half our water bill. Many people think of water as a renewable resource, and it is, but a lot of the water cost is electric energy, so saving water is saving energy. Another advantage of this system is that even if you are using sinks or other fixtures you still get the pre-heat, because my greywater tank stays about 65 degrees, with GFX you only recover energy when the shower is running. The quality of the greywater is monitored every time I flush my toilet too. Where people have high water prices, this system will be more attractive. It should work just about anywhere, except France. This is a very simple system that I expect to last a very long time, and so far I am very happy with it's performance. Thanks, Bob Gagnon

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
    To learn more about this professional, click here to visit their ad in Find A Contractor.
This discussion has been closed.