radiant floor heat??? Yes No Maybe So???

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Geniescience

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Bob NH said:
.... You don't get any real sensation of warming from a floor at 75 degrees F. You get a sensation of warming from a radiant source if the source is at a higher temperature than the target. ....
Very precise. Thank you! I can agree to use the term "a real sensation of warming" as being produced when the source temp is higher than the target temp.

This definition accounts for the shifting point of reference too!

Your outer shell (skin) is at a certain temperature of reference, lower than the temperature of your internal organs. When you put a finger in warm/lukewarm water, it feels warm, and then not, after seconds -- since your fingers have been warmed up to the water temp. The only way for the water to still feel warm is if its temperature keeps going higher than your skin temperature.

Lee, have no fear. A warm floor feels good. Newbies are often concerned it might go "too high"; I've seen it before, and earlier in this thread, I read that "above 85f" might feel too hot. No. You want to be able to turn the floor heat up to 90f and even 95f whenever you want. It is true that it will feel strange to a first-timer who steps onto it with cold feet, but it won't hurt and once they have walked on it a few times they'll like it. As a test, you could put a large tile in hot bathtub water with a thermometer to measure the water temp and then remove the heated tile and ask people to put their weight on it barefoot and tell you what the sensation is like to them. The more they do it, the more they want it hot. Guaranteed. Whether you start out extra hot and go down in temperature, or low and going up, you'll find that their temperature that defines comfort will keep rising until it meets the definition that Bob has provided -- a higher temperature than their feet, by far.

Installing a heat break membrane under the tiles is the means to achieve the end, so the user can enjoy a floor temperature as high as they want when they want.

Quiz: What is worse than a cold tile floor?
A: A heated tile floor that doesn't warm up enough to make you feel like you got want you wanted after all. :)

Lee, don't worry about the internal temperature inside the wire either. I read in this thread or another a remark you made about that temperature. The wire is designed to get hot, just like a toaster filament or an oven heating element, so its core temperature is not to be taken into consideration.

David
 

Randyj

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Interesting conversation. Seems that this analysis concentrates on point of contact and not on what I perceive as being the most important element of radiant heat. IMHO the real benefit of radiant heat and how it works is that the radiating energy travels to the body to achieve that comfort level. The radiant "beam" or "heat wave" is not so much affected by the surrounding air but the heat receptors in the skin translates this into the sensation. IMHO the effectiveness of radiant heat is not in the sensation at point of contact but in it's ability to keep a body warm without moving air and the effect is that the whole room is heated...the sensation of a warm floor is just a benefit of where the source of heat is located...... as my little mind processes ........
 

Bob NH

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Randyj said:
Interesting conversation. Seems that this analysis concentrates on point of contact and not on what I perceive as being the most important element of radiant heat. IMHO the real benefit of radiant heat and how it works is that the radiating energy travels to the body to achieve that comfort level. The radiant "beam" or "heat wave" is not so much affected by the surrounding air but the heat receptors in the skin translates this into the sensation. IMHO the effectiveness of radiant heat is not in the sensation at point of contact but in it's ability to keep a body warm without moving air and the effect is that the whole room is heated...the sensation of a warm floor is just a benefit of where the source of heat is located...... as my little mind processes ........

That was my point regarding the need for higher temperature sources that radiate significant heat to your body so you experience the sensation of being warmed. That occurs only if you have a heat source that is hotter than the body. Heat lamps and high temperature filament heaters can do that because they have low mass to power ratios. Putting heating elements in a tile-over-concrete floor is not going to give you that rapid heating because there is too much mass to quickly raise to a high temperature.

Take a look at the quartz lamp Burda heaters. They are small (typically about 18" long, and 1 to 2 kiloWatts. With a couple of heaters you can step out of your shower and toast yourself on both sides. http://www.theheater.com/english/TERM2000.html http://www.theheater.com/english/Products.html

Heating the walls of the room and other mass is a consequence of releasing heat energy in the room, but doesn't do much to give you a sensation of being warm. It just reduces the rate at which your body loses heat.
 
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I'm not sure how many of you actually have hydronically heated floors so let me describe my bathrooms, which are currently the only heated floors in my house due to the lack of time to put up more solar collectors. Your skin temperature is approximately 90 deg, so for the floor to feel warm it must be greater than that, then up around 100 it will also warm the air to a comfortable level for a naked person, i.e. high 70's. If you can only warm the floor to 85 deg, (due to clouds if you run solar) then the tile will not feel warm, however it won't feel ice cold either.

Rancher
 

Leejosepho

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Bob NH said:
With a couple of [quartz lamp] heaters you can step out of your shower and toast yourself on both sides ...

Heating the walls of the room and other mass ... just reduces the rate at which your body loses heat.

Yes, understood!

Rancher said:
Your skin temperature is approximately 90 deg, so for the floor to feel warm it must be greater than that, then up around 100 it will also warm the air to a comfortable level for a naked person, i.e. high 70's.

I will find out for myself in a few weeks, but I wonder whether you might know how warm/hot a floor can be before it becomes uncomfortable. My thermostat senses both air temperature and floor temperature, and I plan to begin by setting the maximum floor temperature (thermostatic limit) at 85.
 

Randyj

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I'd have to refresh my memory and research but it seems that they run about 120 degree water thru the slabs...I'm not sure how hot the slab gets before the pump turns off or tempering valve starts shooting in cold water but I'm sure it takes a little adjustment to get it to a comfortable level. I'm sure also that using a radiant barrier rather than conventional insulation will make a significant difference.
 

Jadnashua

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Heating a tile floor is one thing, heating a wood floor is another. Most engineered floors, and most solid wood floors shouldn't be heated much above 80-85 degrees, based on what I've read in some manufacturer's spec's.

One of the big benefits of a radiant floor heating system is that you tend to have less stratification and more even heat distribution. There is less air movement than baseboard heaters because the delta-T is smaller - it often doesn't support a strong convection current. As compared with forced air, not having the air movement means that you dont' get as much skin evaporation, and thus, you can often be comfortable with a lower room temperature.

A radiant floor does not respond as fast as baseboard heat or forced air. You might find that with the lower overall temp, you are more comfortable and nearly as efficient to just leave it on - depending on the design, bringing the thermal mass up to temp can be a slow process.
 

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Bob NH said:
Otherwise, you will be spending a lot of money heating the earth, which is a VERY LARGE heat sink.

LOL! Heat sink...funny :D

Oh Yeah, was the consensus yah or nah to radiant floor heat. I got lost in some of the detailed posts. Can anyone summarize? I was thinking of using it in the other bath remodel.
 
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Leejosepho

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Here are some pictures of our bathroom floor project so far. I have used 1/2" concrete board with thinset both under and over to prepare a solid and smooth surface, with the concrete board being nailed every 4 to 6 inches. I chose loose wire rather than a mat in order to heat more area than a dimensioned mat would have reached, and the white paint made it easier to see the wire layout first drawn on the floor as well as to prepare a good surface for the foil tape actually holding the wire in place.

Applying the foil tape over the wire as I went along was a bit tedious, but the radiant effect gained and confirmed during testing easily justified my own time and expense for the foil tape. The next step is to now place a scratch coat of thinset over the entire floor area so my son-in-law and I will have a smooth surface for actually laying the mosaic tile. Also, and since there is no heating wire in the areas for the toilet, vanity cabinet and tub, I have since added screed rails (taped-down scrap wire) in those areas to help assure flat surfaces overall.

To circumvent any future dilemma of tearing up tile to replace a floor sensor, the sensor wire has been pulled through a small tube that will push the sensor down into a piece of 3/8†plastic tubing embedded in the floor in a place that will not see heavy foot traffic.

Helpful comments, suggestions and questions are always welcomed!
 

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Jadnashua

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Screeding thinset works and is fairly inexpensive, but self-leveling concrete (slc) is faster. Check it out, then decide.
 

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jadnashua said:
Screeding thinset works and is fairly inexpensive, but self-leveling concrete (slc) is faster. Check it out, then decide.

I had started out with plans to use an SLC, but the folks at the big store where I usually go told me their particular brand still actually needed to be troweled. Since they were out of it at the time anyway, I tried another "patch" mix they had, but that stuff kicks way to fast for use on a large surface requiring much volume. Thinset is, at least for me, impossible to trowel to a smooth finish, but I have a "holy stone" -- you use it on your knees (see picture below) -- for taking care of that. But, maybe I could/should have looked around a little more before settling on the thinset.

Randy: I thought you might like to know the outcome of a test I did after actually placing two sensors in my floor, with one of them imbedded (as in the above picture) and the other simply foil-taped to the surface of the concrete board. With my heating wire energized, the two sensors remained within about .5 ohm of each other during the duration of my 30-minute test. The one imbedded in the floor felt warm on top (but was likely cool underneath) and the one on top of the concrete board felt cool on top (while obviously picking up heat from the floor). Point: A removeable sensor in a imbedded tube seems to do just fine.
 

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Jadnashua

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A medium bed mortar can be applied in one layer up to around 3/4". A thinset should not be installed at greater than about 1/4" in one layer. Otherwise, you'll probably end up with cracking and extended cure times, so keep that in mind.

SLC is mixed very wet, and other than to push it into corners and wet the surface, requires little to no troweling. It also does kick off fast and the preparation is crucial to a good result, but is manageable.
 

Geniescience

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non smooth thinset is OK as a scratch coat.

lee do you have to smooth out thinset? I just used a toothed trowel, and that puts a certain quantity everywhere. It ensures that the height gain is equal everywhere. All you are trying to do is to ensure that the wires do not become barriers on tiling day. The actual tiling surface does not have to feel smooth later, when you come to tile it. You are going to cover it again with thinset all over again.

david
 

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geniescience said:
lee do you have to smooth out thinset? I just used a toothed trowel, and that puts a certain quantity everywhere. It ensures that the height gain is equal everywhere.

I am using a regular trowel while letting the wires act like screed bars for the moment so they cannot possibly be "barriers on tiling day", as you have described. My use of the stone is simply about getting rid of the occasional ridge left over from my best attempts to trowl the thinset.

geniescience said:
The actual tiling surface does not have to feel smooth later, when you come to tile it. You are going to cover it again with thinset all over again.

Sure, and I am certainly not looking for a glass finish here. At the same time, and maybe you can help me here, I will be putting down interlocking 12" x 24" mats of 2" hex mosaic tile. So, one of the reasons I am going for "flat and straight" well before I actually lay the tile is to avoid "waves" all across the finished floor, and my question is how to lay those flexible mats of tile in such a way that they end up at least as flat as my preparatory work. Is there some technique or device (such as something like a small bull float) the pros use to press all those little tiles down together and evenly? Also, what do I have to do about all the thinset that will be oozing up around all of those however-many little tiles?

Here is a picture one of the mats with a roll of electricl tape underneath:
 

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Jadnashua

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When I recently layed some tile similar to yours, I used my grout float to beat it in place. If you have a very flat floor and the backs of the tile aren't cupped so they need a fair amount of thinset, then you don't need a very big notched trowel which will limit the oozing up into the tile. Since you are dealing with a light colored tile, get some white thinset (unless you are going to use a dark grout) so it doesn't show as much if you do miss something. The white costs a little more because it is harder to get the materials, but it also isn't as messy looking under your fingernails, too!
 

Geniescience

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on the right track

seems like we both have similar views on the complexity. Wires are screed; goal is to be flat enough to tile on later.

you are right that 2"x2" tiles need a very flat surface. I "kinda" forgot that someone might use small tiles... I use big tiles.

I'd be scratching off bumps and adding more thinset, for days. A straightedge and a level, on my knees. No ridges that the hexagonal tile makes more apparent. This is one time I'd say yes even to SLC as final prep, on top of the screeded thinset. (How level is your floor across its length and width? SLC may not be the right product...)

BTW, do you know that small tiles can move (slide) for many minutes after you lay them in thinset? Just use a matching color grout and the thickness variation in your grout lines will not be apparent. This is not related to the bumpiness of your floor; it's just another thing to consider.

david
 
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Leejosepho

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Thank you gentlemen, for the confirmations and added insight. A mechanic at work who lays tile on the side has said much of the same. Overall, I plan to do as much prep as necessary to get a smooth and flat surface for the floor's cover layer of tile, including trying to build the surface up at least 1/8" or so above the heating wire. Then, I will use a trowel with relatively small v-notches while actually laying the tile. At that point, pressing it down a bit without causing depressions should not be a problem, and I will probably try to use some kind of hard-backed stiff-sponge pad (with a density such as that of a sanding pad). And if sliding becomes an issue, I should be able to temporarily stake the mats with some small finish nails. Oh, and the backs of the individual tiles are flat with some light "grip rings" or whatever those raised features might be called.

I had not heard of the issue as to mortor and grout. The grout I intend to use is a fairly dark, grayish blue, so I suppose the darker thinset would be best.

At the moment, most of yesterday's even-with-the-top-of-the-heating-wire (about 3/16") coat of thinset is looking "mostly dry", so I should be able to have another go at it tomorrow evening.

Thank you!
 
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