How to make a warm floor using a hot water pipe?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Eddie Ebron, May 15, 2019.

  1. mliu

    mliu Member

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    To paraphrase a well-known proverb, "You can lead a man to knowledge, but you can't make him think."
     
  2. DIYorBust

    DIYorBust Member

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    You cousin could probably also use the snow melting shower up here.
     
  3. plumber69

    plumber69 In the Trades

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    This post really got me thinking, if I was to run a hot 1/2 pex up to the attic then strap loops right below the roof, say about a 350 foot run, then it would feed my dishwasher. This would melt all the snow off my roof when I did dishes. Of course I would use heat teansfer plates.
     
  4. Dana

    Dana In the trades

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    For even a fairly small floor it will take at least 50' of half inch PEX to heat the floor even at a high duty cycle (as in "longer than a 10 minute shower). At 2 gpm every 50' of half inch PEX is going to add about a half minute delay to when hot water arrives at the shower.

    The thermal time lag between the heat going into the slab and the surface temperature rising is substantial, even when running continuously. For the small amount of heat delivered during a 10 minute shower the miniscule peak rise in surface temperature will occur after you've already dried off, had breakfast an headed out for work.
     
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  5. plumber69

    plumber69 In the Trades

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    Dont turn your bathroom fan on while you shower, the steam will heat the floor better the running a pipe thru. You probly will only be running 1 gpm of hot water thru the shower head. At 10 minutes, thats only 10 galons. Your floor temp might rise .001 degrees
     
  6. mliu

    mliu Member

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    If you really dislike stepping out of your shower onto cold tile, there's an inexpensive but effective solution that does not require turning your home's plumbing into Frankenstein's monster.

    [​IMG]
     
  7. Tuttles Revenge

    Tuttles Revenge In the Trades

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    If you ran a hot water recirculating system through all of it might help.. I know that open systems where the domestic and heating water come from the same source the circulating pump fires each day for 15 minutes to avoid stagnate water and legionella bacteria build up. Keep the loop at least a foot from your toilet so it doesn't melt the wax ring. Personally I'd rather run it through a towel warmer that i've got a bathrobe and slippers on..

    leaks.. meh.. its unlikely because you will have Zero fittings in the slab. I've run thousands of miles of PEX and never seen a leak that wasn't from some external thing.

    But most of the negative comments are really baseless. The concept is odd and most people don't like stuff they're not used to.
     
  8. DIYorBust

    DIYorBust Member

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    That's a plausible idea, probably easier to put the electric system in.
     
  9. Eddie Ebron

    Eddie Ebron New Member

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    Sir, you are right) Nowbody wants to create)) But I ve found very ineresting vido on Youtube. abour how to radiant the floor by hot water pipes



    So,, very detailed instuction. It is not ads from me NO, just a good video
     
  10. DIYorBust

    DIYorBust Member

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    Please take pictures, and let us know how it turns out!
     
  11. Dana

    Dana In the trades

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    I'm very accustomed to radiant floor heating, and prefer to see the math. A radiant slab with embedded PEX isn't a way to quickly raise the surface temperature during a shower.

    Even at the 99% design heat loads of a bathroom in central Florida the floor temps won't need to be very warm, making full radiant floor heating not particularly attractive, but sure you can do it, even using the water heater, though isolating the potable water from the heating water with a plate type heat exchanger would be preferable. That's not a particularly rare thing to retrofit in the northeast, where 99% outside design temps are in single digits F above/below 0F (compared to north of 40F for the Orlando area.) If one wanted to design a radiant floor heating system for the bathroom using only a small piece of slab/floor as the heat emitter so that the temps are warm enough to matter for bare feet that's fine, but don't use the hot water flow to the shower as the heating system water- it only adds complexity to the design.

    And don't hack it- design it. Start with a Manual-J heat load calculation for the room, and adjust the radiating area & surface temperature needed to deliver the design-condition heat to the room with the amount of radiant slab you intend to have. Tweak the area such that even at design conditions (42F outdoors for Orlando) the surface temp of the patch heating the room isn't much more than 90F (or it will be the opposite of comfortable when it drops below the 99% outside design temperature), but not less than 80F (or the barefoot comfort benefit during average wintertime heat load conditions won't be enough to matter.)

    Heating a small patch of floor intermittently & quickly for barefoot comfort while stepping out of the shower calls for an electric mesh under the tile solution, not a full-on slab heating solution (whether using a recirculation pump or not.) The time lag of the thermal mass of the concrete is real. That lag becomes considerably smaller if the heat is being applied 3/8" below the surface of the tile rather than 2-3" below. The efficiency hardly matters- in my area residential retail electricity is about twice that of Florida, but intermittent heating (or even the room heating) of small bathroom floors with resistance mesh heating usually pencils out favorably against hydronic solutions backed up by condensing gas boilers. The "payoff" of lower heating costs with a full room heating solution vs. just heating a patch of floor with electricity briefly when needed just isn't there when the space heating load for the room is so miniscule.
     
  12. mliu

    mliu Member

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    I too am familiar with radiant floor heating, having years ago designed and installed a dual-zone electric grid radiant floor system in the entertainment room of a multi-million dollar mansion in California. As I recall, the slab was prepped & primed, the electric mat was affixed to the slab, then we poured a 1/4"-3/8" layer of self-leveling compound, and finally, it was tiled. The negative comments in this thread are not baseless; they are based on experience and an understanding of thermodynamics. And it's not that we don't like the concept of heated floors, it's that we don't like hair-brained DYI hack jobs that may seem like a good idea but are not.

    Dana is 100% correct: if you want a heated bathroom floor, do it right. A properly designed hydroponic system is expensive and very slow to heat due to that thickness of the floor (thermal mass) required to accommodate the tubing. it is appropriate for heating your home over a long period of time. It is not appropriate for quickly heating your bathroom floor so you can step out of your shower in comfort. An electric grid system is the correct solution if the OP really wants to warm his bathroom floor. But even that will require pre-heating well in advance of taking his shower. So it will work if his showers occur on a regular schedule (like in the morning before work) because the controller has a timer can be set to begin heating an hour or so before shower time. However, it likely will not provide much benefit for spontaneous showers.
     
  13. Eddie Ebron

    Eddie Ebron New Member

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    О, I will think about of course) It was my "great idea", but you are right. We should not waste our time in the life for such... great "great ideas", Thanks everybode. I see you are really professionals here)
     
  14. Reach4

    Reach4 Well-Known Member

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    IL
    While you are looking for a novel way to do this, you could have a hot water recirculation system that is controlled by a switch. Activate the switch, and it runs a recirculation pump for 15 minutes or whatever. Then before the shower, start the recirculation. The recirc water goes through the buried pipe to warm your floor area. Bonus is that the water from the shower will be hot almost instantly after the recirculation has started.

    Electric would be easier.

    I am not a professional.
     
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