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

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Eddie Ebron

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I have one great idea how to make a warm floor in my bathroom using running hot water. So... from the boiler to the shower i am going to put the hot water pipe in the floor, cover pipe by metal grid and a concrete and tile. So, while I get a shower my floor is warming. I have just a doubt what kind of pipe to use for this? What thikness of the concrete layer to use so that is not hot for feet? What is the best way to lay the pipe?
 

Dana

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But maybe the drain water could be used?

The drain water is going to be 95-100F, so sure it would be plenty for heating a floor to non foot-frying temperatures, but getting the heat transfer without pressure behind it would be an issue, as would the cleaning protocol should it become clogged.

Unless the floor is very large it's unlikely that the floor will ..."steal" all the heat from the hot water pipe...". Unless you have the largest bathroom in Florida and want to heat the whole floor that's not the issue. The bigger problem would be getting heat into the slab fast enough to make a difference in feel to bare feet. At a typical 2 gpm shower flow and FL type incoming water temps is about 50,000 BTU/hr in winter (less for most of the year) and the conductivity of concrete/gypcrete isn't all that high- it takes quite a bit of PEX tubing to pull even 5000 BTU/hr out of the tubing with 120F water. The thicker the slab the slower it will heat up- it's not clear that it would deliver the floor temperature you're looking for at the end of a 10 minute shower. You'd also be heating the floor in summer when it's 95F outside, which isn't exactly the goal in FL.

Read up on how to design concrete radiant heating slabs- a serpentine of half-inch PEX embedded in a 3" slab with a foot between loops of pipe wouldn't drop the temperature of the water reaching the shower mixer by even 10F, but it would take a pretty long shower to make the floor warm enough to matter.

On the other hand, low voltage electric mesh radiant under the tile can warm the surface temps noticeably over a typical showering time.
 

plumber69

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I have one great idea how to make a warm floor in my bathroom using running hot water. So... from the boiler to the shower i am going to put the hot water pipe in the floor, cover pipe by metal grid and a concrete and tile. So, while I get a shower my floor is warming. I have just a doubt what kind of pipe to use for this? What thikness of the concrete layer to use so that is not hot for feet? What is the best way to lay the pipe?
Im not sure if your serious or not
 

WorthFlorida

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I checked your zip code and you're about 20 miles from my home on the other side of Orlando. Yes, there are those few days of the year that weather gets chilly and having concrete under the tile floor can be made more comfy. After spending a whole lot of money on the remodel of our master bath, the natural marble floor can be a bit chilly and I'm kicking myself for not thinking about it.
If you really want a warm floor go with an electric grid. It's easy, low cost and won't steal heat from your shower. You'll be able to switch it on and off at any time of the year. When we have our summer 95 degree days you don't want to dump heat into the home for the AC to take it back out.

shopping
 

jadnashua

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There are all sorts of floor warming systems out there from a mesh customized for your space, to free cables you wind back and forth, to systems designed to aid while tiling, as well. Many of those systems are a pain to then get tile to set evenly afterwards. There are a couple of mat systems designed to avoid that issue, like DitraHeat.

 
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Eddie Ebron

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The floor will "steal" all the heat from the hot water pipe, so, you will "eventually" have a warm/hot floor but a cold shower.
Oh, I thought about and I think the won't "steal" the heat from the hot water, because I want to make a small part of the floor. Just nearby bath. I thint it will be not more than one sq ft.
 

Eddie Ebron

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The drain water is going to be 95-100F, so sure it would be plenty for heating a floor to non foot-frying temperatures, but getting the heat transfer without pressure behind it would be an issue, as would the cleaning protocol should it become clogged.
Absolutely agree, it will be impossible to clean(
 

mliu

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Why do you think so, Sir?
A partial list:
  1. Embedding your shower's water supply lines in concrete is an invitation to disaster. Imagine the cost involved if there is ever a leak. And until you repair it, no water for your shower.
  2. Unless you take showers that last for hours long, the heat transfer through the concrete and tile will probably be too small for you to effectively heat your floor. In other words, you will still be stepping out onto cold tile. Typical hydronic radiant floor heating systems, that constantly recirculate hot water, can take several hours to over a day to get the floor up to desired temperature.
  3. In the meantime, you're cooling your hot water supply to the shower. So now you must use more hot water to get your desired shower temp.
  4. Which means that it will take considerably longer for your shower to come up to temperature. All that cold water will have to be drained from the piping in your floor before your shower is ready to use. What a waste of water.
  5. And since you have absolutely NO CONTROL over this makeshift system, you will be heating your floors even on the hottest days of summer.
Need I give more reasons?
 

Eddie Ebron

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Unless the floor is very large it's unlikely that the floor will ..."steal" all the heat from the hot water pipe...". Unless you have the largest bathroom in Florida and want to heat the whole floor that's not the issue. The bigger problem would be getting heat into the slab fast enough to make a difference in feel to bare feet. At a typical 2 gpm shower flow and FL type incoming water temps is about 50,000 BTU/hr in winter (less for most of the year) and the conductivity of concrete/gypcrete isn't all that high- it takes quite a bit of PEX tubing to pull even 5000 BTU/hr out of the tubing with 120F water. The thicker the slab the slower it will heat up- it's not clear that it would deliver the floor temperature you're looking for at the end of a 10 minute shower. You'd also be heating the floor in summer when it's 95F outside, which isn't exactly the goal in FL.

Read up on how to design concrete radiant heating slabs- a serpentine of half-inch PEX embedded in a 3" slab with a foot between loops of pipe wouldn't drop the temperature of the water reaching the shower mixer by even 10F, but it would take a pretty long shower to make the floor warm enough to matter.
Thanks a lot for your detailed answer. First of all I am really wonder that you recommend me to use half-inch PEX that I chose!)
About you data I will read more, I need to calculate and think a little.

About temperature in FL, I understand, but my cousin just bought a house in NY and also wants to make such a floor)))! I think I should make a switch so that the water can run right into the shower or move through the floor. If I need to heat it.

Anyway, you made me think about more details!!
 

Eddie Ebron

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There are all sorts of floor warming systems out there from a mesh customized for your space, to free cables you wind back and forth, to systems designed to aid while tiling, as well. Many of those systems are a pain to then get tile to set evenly afterwards. There are a couple of mat systems designed to avoid that issue, like DitraHeat.
Thanks a lot) But I would like to make me sure with my idea. That's why I try to avoid in the future possibl problems
 

Eddie Ebron

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A partial list:
  1. Embedding your shower's water supply lines in concrete is an invitation to disaster. Imagine the cost involved if there is ever a leak. And until you repair it, no water for your shower.
  2. Unless you take showers that last for hours long, the heat transfer through the concrete and tile will probably be too small for you to effectively heat your floor. In other words, you will still be stepping out onto cold tile. Typical hydronic radiant floor heating systems, that constantly recirculate hot water, can take several hours to over a day to get the floor up to desired temperature.
  3. In the meantime, you're cooling your hot water supply to the shower. So now you must use more hot water to get your desired shower temp.
  4. Which means that it will take considerably longer for your shower to come up to temperature. All that cold water will have to be drained from the piping in your floor before your shower is ready to use. What a waste of water.
  5. And since you have absolutely NO CONTROL over this makeshift system, you will be heating your floors even on the hottest days of summer.
Need I give more reasons?
I wrote to another man that I will think about ....mmm.. some water flow switch? to avoid to heat the floor all the time. And I wrote above: Oh, I thought about and I think the won't "steal" the heat from the hot water, because I want to make a small part of the floor. Just nearby bath. I think it will be not more than one sq ft.

And you make me think about: I have to take into account the distance that water passes from the heater to the shower. THANKS
 

Eddie Ebron

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LOOK! But probably this is better?
Happybuy 656Ft Roll of 1/2" PEX-AL-PEX Tubing Oxygen Barrier Radiant Floor PEX Pipe Radiant Heat Floor Heating Plumbing 200M Inner Aluminum Layer PEX Tubing Pipe (1/2" O2-Barrier, 656Ft/White)

  • Total Length: Approx. 656ft(200m); Overall Thickness: Approx. 0.08"(2mm); PEX Thickness: Approx. 0.067"(1.7mm); Aluminum Thickness: Approx. 0.008"(0.21mm); Interior Diameter: Approx. 0.47"(12mm); Exterior Diameter: Approx. 0.63"(16mm)
  • Pressure Range: 870~1160 psi (6~8Mpa); Working Temperature: -40℉~203℉(-40℃~95℃); Continuous Working Temperature: 158℉(70℃)
  • PEX-AL-PEX tubing involves two special polyethylene PEX layers(Its cleanness, non-toxic and smoothness assures long-term usage) and an aluminum layer sandwiched between them(Its aluminum layer ensures resistance of gas infiltration which is perfect for closed loop radiant heating systems)
  • PEX tubing gains the advantages of metal and plastic tubes, suitable for home decoration and can be applied for domestic water, condensate water, oxygen, compressed air and other kinds of chemical liquid
  • Radiant heat pex has the ability to bend and can stay the way it was bent(very little recoil due to the aluminum layer); Features durable heat resistant primer to provide superior adhesion performance, ensuring the three layers to behave as one over the service life
 
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