Using DHW for spot/limited area radiant heat

Discussion in 'Water Heater Forum, Tanks' started by mark_g, May 4, 2009.

  1. mark_g

    mark_g New Member

    Mar 3, 2009
    I recall reading somewhere about running the DHW supply in loops under a bathroom floor to act as a mini radiant system en-route to lavs, sinks, etc. In the article, the installer used it for small area floor warming, and it did not reduce the spout temp of the water adversely.

    We're completing roughs and wonder if anyone has has real world experience with this and can offer advice. We're not looking to heat the bathroom, just remove the chill from the key parts of the floor. Our DHW is being plumbed with tank, return and (hopefully) gravity feed--prefer no pump though maybe here it will be needed.

    I wonder if response time to heat the floor will be too long, and for these spot applications, to embed some electric under the tile and be done with it.

    Thanks for feedback or references to sources.

  2. leejosepho

    leejosepho DIY scratch-pad engineer

    Nov 23, 2006
    disabled-retired industrial fabricator
    200 miles south of Little Rock
    Electric heating wire is what I have, and it works great! I once had the same idea you have read about, but about the biggest thing you might heat with the water running to a shower is a towel warmer. However, a recirc line with a small pump and a thermostat (sensor) in the floor would be relatively inexpensive to install, easy to maintain and quite effective without (as you already know) affecting water temp at the faucets.
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  4. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    You do not get anything for free. If the pipes are going to do any kind of effective heating, they WILL lose temperature in the process. As the area absorbs heat from the piping, the amount of heat lost will be reduced, but that will only occur once the floor is up to, or close to, temperature. It is an idea that is neither good for heating, nor ideal as far as the water temperature at the faucet is concerned. One thing you can be sure of, however, is that if the water is arriving at the sink with little loss of temperature, then it was doing a lousy job of heating the floor.
  5. kingsotall

    kingsotall Plunger/TurdPuncher

    Aug 17, 2008
    Hand copper part cleaned ready to go
    Flagstaff, AZ Sitting on an upside down 5 gallon b
    Of course someone has to throw in the obligatory Legionella concern, so I'll do the honors.
    Stagnant water at certain temps. (hot water line) can be a breeding ground for microbes such as Legionella. You have a recirculation system so I don't think you have much to concern yourself with.
  6. SewerRatz

    SewerRatz Illinois Licensed Plumber

    Nov 20, 2008
    Chicago Illinois Licensed Plumber
    Chicago, IL
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