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nocry
01-25-2007, 06:13 PM
So what is the consensus out there about radiant floor heat???

I am doing a gut rehab of a full 7' x 8' main bath in a townhome and would be able to install a 2' x 8' run of floor heating coils...

is it worth it??? what are the pros??? the cons???

if it is worth the investment, what brand would you guys recommend???

thanks!

jadnashua
01-25-2007, 06:32 PM
Radiant heat is nice in a tiled room, especially a bathroom where you'll be barefoot. But, about the most you can get out of it is around 15W/sq ft, so don't expect to really heat the room with it, only take the chill off of the floor. If you want more heat, then maybe hydronic heat. But, as a result of somewhat limited heat, you can run it in the summer, too, and not create a huge load on the a/c. My unprofessional opinion...

A heated towel bar is a really nice touch, too! Again, unless you go hydronic, they only use around 150W or so.

leejosepho
01-27-2007, 09:07 AM
Radiant heat is nice in a tiled room, especially a bathroom where you'll be barefoot. But, about the most you can get out of it is around 15W/sq ft, so don't expect to really heat the room with it, only take the chill off of the floor. If you want more heat, then maybe hydronic heat ...

Honest question: Why would a hydronic floor-heating system heat a room where an electric system would not?

Once a given floor area has been warmed to a desired or tolerable temperature, and assuming either system is capable of maintaining that temperature, I cannot see how the source of the heat would affect how well or how much a warmed floor might radiate heat into the space either above or below it.

jadnashua
01-27-2007, 12:21 PM
You can circulate a lot more heat through the tubing than you can tolerate creating in the electrical resistance wiring. From what I've read, you can get a max of 15W per square foot from electrical resistance heating in a floor - enough to take the chill off of the floor, but not likely enough to heat the room. That's not much. Lets say you can circulate 2 gallons of water through the tubing per minute - that's about 16 pounds of water, and lets say that coming in, it is in the order of 130 and drops to 90 on the way out, that's 40 degrees * 16 pound, or 640 BTU/minute. That's equal to 11.25KWh. You'll never get that from resistance wiring. Water can hold a lot of energy more easily than a hot wire.

leejosepho
01-27-2007, 04:15 PM
Lets say you can circulate 2 gallons of water through the tubing per minute - that's about 16 pounds of water, and lets say that coming in, it is in the order of 130 and drops to 90 on the way out, that's 40 degrees * 16 pound, or 640 BTU/minute. That's equal to 11.25KWh. You'll never get that from resistance wiring. Water can hold a lot of energy more easily than a hot wire.

I definitely understand that, and maybe my problem here stems from an incorrect belief that I can maintain an 80-degree (or whatever number) floor temperature with 15 watts per square foot of heating wire. But if I can, then the matter of heating any space above the floor is one of heat exchange and loss, and not one of how the heat is actually supplied. As compared to the hard work of heating wire, only a small amount of tubed hot water might be required to heat a square foot of floor to a given temperature, but then the question is whether or not that square foot of floor (a heat exchanger) can release the supplied heat fast enough to keep the space above it warm.

jadnashua
01-27-2007, 05:08 PM
Without knowing what you heat loss is from the room, you'll never know unless you try it, and then its too late to change...

leejosepho
01-27-2007, 05:17 PM
Without knowing what you heat loss is from the room, you'll never know unless you try it, and then its too late to change...

Yes, and that is why I next intend to try to find out how to make the floor as efficient as possible in the exchange of heat!

Do you know of a typical or usual and comfortable floor temperature used by any kind of floor-heating system being used to warm a room? I am assuming a surface temperature of 80-85f degrees would be about the highest that would be comfortable, at least for bare feet.

Randyj
01-29-2007, 06:21 AM
One thing most people do not understand is that there is a very big difference in the physics of radiant heat v.s. conditioned air heat. The heat travels to your body so to speak while the room air itself may not be warm. Yet, it is much more comfortable heat. To be able to design and utilize radiant heat it really helps to study what radiant heat is. E-foil a.k.a. double bubble uses the principle to give it the insulating quality it has. In explaining how this "foil" works it is usually stressed that it is totally different than insulation in that insulation impedes the flow of heat whereas the foil reflects the heat therefore keeping it inside the structure...or out of the structure. Heated walls and floors will radiate heat. If you heat the air then it is absorbed into the walls and runs right out the doors, windows, etc. Much of it is principle & theory but understanding it helps planning & design.

leejosepho
01-29-2007, 01:05 PM
... a very big difference in the physics of radiant heat v.s. conditioned air heat ...
... double bubble uses the principle to give it the insulating quality it has. In explaining how this "foil" works it is usually stressed that it is totally different than insulation in that insulation impedes the flow of heat whereas the foil reflects the heat therefore keeping it inside the structure...or out of the structure.

Yes, and I am slowly catching on to that! I purchased some "double bubble" on my misunderstanding that it would do well under the concrete board in my bathroom, but when I read its application instructions, I began learning about what you are saying here. Not only would it be ineffective when not being used to confine a given volume of air, but my concrete board would have been applied on top of something soft! Bad idea all around.

So, I now plan to simply install the concrete board and build up from there (including the heating mat), and to then use the double-bubble to close in the bottoms of the floor joists, thereby making a bit of a "heat box" through which I will run a few loops of copper supply line to my water heater. Even if I only get a few degrees out of that, it will be "free heat" to give the water heater a jump start, eh?!

geniescience
01-30-2007, 03:05 PM
use an underlayment made of cork or synthetic under the tiles, as a heat break. Prevents thermal bridge. Puts the heat cables energy into the tiles, not into the floor underneath.

david

leejosepho
01-31-2007, 02:04 PM
use an underlayment made of cork or synthetic under the tiles, as a heat break. Prevents thermal bridge. Puts the heat cables energy into the tiles, not into the floor underneath.

That had been my first thought, and I would certainly agree as to that being a good idea in many, or even in most situations. However, and since the heating wire I have was specified for "deep heating" a thick concrete slab during off-peak hours, I am more inclined to at least give it an opportunity to heat more than a 1"-or-so tile floor.

Bringing these thoughts over from another thread:


Is it linear? I can't figure out what it might mean to say that "anything less might actually..." I think it is linear, to apply the same power (i.e. heat energy) onto a smaller area produces a linearly increasing impact. Close correlation to the temperature you feel.

What I was saying is that placing the wires too close together would be the same as placing hydronic tubes side-by-side, thereby leaving insufficient "breathing room" for the heat to dissipate as quickly as supplied.


The amount of mass to heat is hard to simulate with loose cables. Once you put a little bit of thinset on them, to make a flat surface to tile onto, you will see that they don't have nearly as much impact. Then, once you have tiled them, the effect will be a huge factor less. Because of the new thermal mass to heat.

Yes, understood.


Use a non-heat-conducting tile underlayment as a thermal break, and your heat will find its way into the tiles first before it goes down into the subfloor and the rest of the building. This is the best way to ensure you get a faster response and more heat where you want it.

In my own case, "response time" is not a concern. It will take whatever time it takes to heat the floor to a pre-set temperature ... and what happens after that is what I am hoping to effect by constructing an as-efficient-as-possible "heat exchanger" that happens to look like a bathroom floor. It might take an hour or more to heat the floor, but my thoughts here are about where and how quickly the difference between the "get there" energy and the "temp maintenance" energy will go after that.


My thoughts on the upper limit of watts per Sq Ft : umm, it is a rule-of-thumb that has become a norm, which includes a big margin for safety. So, it is conceivable that you can put cables a touch closer and get more powerful, without risking any adverse consequences. I have heard this first-hand from the most experienced installer of the oldest electric heat cable company i know of. I have done it myself, to put more heat in a part of my floor nearest to the exterior wall. Use your mechanic's horse sense; be prudent not daring. I trust you will do the right thing. This is not advice for the next reader to follow.

According to the man who sold me a couple of thermostats a couple of days ago -- we are doing two bathrooms here -- the matter of 15 w/sf is about not being able to make the floor uncomfortably warm ... or along the line of safety you have mentioned, to not be able to melt a vinyl floor or cause spontaneous combustion within carpet! But if you have a high-efficiency "heat exchanger" for processing the supplied heat, whatever its source, then the same levels of comfort and safety could be maintained even at higher wattages per square foot.


The spacing between the wires is the only thing you can vary, so use it to get the heat layout you want. Avoid overheating the base of your toilet; do not try to get a warm toilet, since a weak seal (wax ring) might be weakened further if warmed up.

Thank you for the thought about the wax ring! I was planning to stay at least 3" away from anything, but now maybe more than that around the toilet.


Some people have been known to put floor heat cables into portions of their walls, and tile over that too. The only adverse thing is that no-one in the future should ever try to drill into that "wall" surface, as they will be risking hitting a cable. The same applies to anyone who wants to drill into a heated floor.

Yes, and I intend to take pictures of certain spots for that kind of reason ...

At a large auto dealership here where I happen to live, the entire floor of its new building has waste-oil-fired hydronic heat. But after the concrete crew missed placing the bolts for the front-end alignment rack, that rack later had to be cemented to the floor to avoid the risk of drilling any holes for anchors!

geniescience
01-31-2007, 04:58 PM
ok, it's obvious you have this all thought out.

A thicker amount of concrete is OK, if it be your wish. The heat transfer to the room will not be faster, i.m.o., because it is just more mass to heat, more deadweight, like a flywheel evening out highs and lows a bit, which you don't need. It won't speed up heat transfer to the room. Besides, you are going to leave the floor warm as a regular state. It makes no difference that the cable is a 208Volt cable. Also probably no difference: that it was "designed" in some way to be embedded in slabs, which to me means that its outer sheath (a grounding insulator) will be designed to hold up well against caustic wet curing concrete and thus it has no bearing on the stable steady state that you will have once your installation is done.

It is OK to put the cables much closer than 3" to walls. I really really doubt you will get the heat in the floor up to any level that anyone will deem uncomfortable, even if it might be higher than 85 Fahrenheit. People like having their toes toasty warm. Toilets can be sealed with non-wax rings now, so you could run no risk even with a heated toilet base, i.m.o. I would design a floor layout with a cable running as close as possible to the perimeter, not 3" from it. Before anyone reacts too strongly to what I just said in these last three sentences, read the next paragraph.

The Aubé company makes good thermostats with good features; it will do the job that a flywheel would, so you don't need more thermal mass. Thermal mass is important in a hydronic system (slow to react, high water temperatures), and not in an electrical cable system. The thermostat is what keeps your floor at the temperature you desire, regardless of whether the cables are real close together, or right against the wall or the toilet, or whether your floor has high or low thermal mass. Let the thermostat bring the floor temperature up to the level you feel comfortable with, and DON'T ever worry about the floor potentially being too hot to handle -- that is what the thermostat is regulating; how can I say that more clearly? . BTW, Lee, you didn't mention buying a probe, but i guess that came with the thermostat, right?.

So based on all the bove, I hope to have made a clear case why it is a good idea not to attempt to re-create a slab even tho' the cables were initially designed for another application. Let the thermostat do the thinking; it trickles out the right current to suit the heat needed. Ask Aube, for confirmation. Just focus on isolating the heat from losses. There is likely to be an external wall and a subfloor connected to the outside wall structure... and this is a small permanent invisible heat loss. A heat bridge.

I need to repeat the importance of a heat insulator if you want to ensure you get the most efficient heat in the room and the highest temperatures. You could use 1/2" Wedi board. Or cork. Or XPS foam. Or a sound proofing membrane, a felt-like type.

Heat loss in the room will depend on air transfer (minor air currents due to convection) and on the heat bridging in your subfloor. If the floor heat is not in contact with a heat-conducting subfloor, if doors are closed, if there are no air leaks, and if you have a generally well-insulated house, then the room will get very warm. That may be overkill. If you install the cables on CBU directly on top of a wood subfloor, the room will still get warm. How tightly your building is insulated is also a factor, since the heat loss (gradient) of the whole building is a factor in the room's heat loss.
http://en.wikipedia.org/wiki/Thermal_insulation
http://en.wikipedia.org/wiki/Thermal_bridge
http://en.wikipedia.org/wiki/Building_insulation


david

leejosepho
01-31-2007, 05:15 PM
A thicker amount of concrete is OK, if it be your wish. The heat transfer to the room will not be faster, i.m.o., because it is just more mass to heat, more deadweight, like a flywheel evening out highs and lows a bit, which you don't need. It won't speed up heat transfer to the room. Besides, you are going to leave the floor warm as a regular state.

Yes, we are thinking alike there. And when I talk about heat transfer, I am talking about looking into any "heat-exchanger" differences between qualities of ceramic tiles.


It makes no difference that the cable is a 208Volt cable. Also probably no difference: that it was "designed" in some way to be embedded in slabs, which to me means that its outer sheath (a grounding insulator) will be designed to hold up well against caustic wet curing concrete and thus it has no bearing on the stable steady state that you will have once your installation is done.

We again agree.


would design a floor layout with a cable running as close as possible to the perimeter, not 3" from it.

Okay, I likely have enough cable to go closer!


Thermal mass is important in a hydronic system, not in an electrical cable system.

Why so?


Lee, you didn't mention buying a probe, but i guess that came with the thermostat.

Yes, and I bought an extra one for each system in case an original ever fails. Also, the stat man told me he had just read some literature from a company providing a short piece of some kind of tubing that can be used for installing sensors in removeable ways.

geniescience
01-31-2007, 05:28 PM
so some of the answers are now in the first post,,

About the best tiles to ensure heat transsfer: once you get into the range known as Porcelain (not Ceramic) you have gotten the best for heat transfer. There is not much difference anyway.

david

leejosepho
01-31-2007, 05:39 PM
Thermal mass is important in a hydronic system (slow to react, high water temperatures), and not in an electrical cable system.

Thermal mass is necessary if one is storing heat for later, but thermal mass (including the nature of any material other than copper) is actually why a hydronic system is slow even if its water temperature is higher than that of an electric system, correct?


Let the thermostat do the thinking; it trickles out the right current to suit the heat needed. Ask ... for confirmation.

Oh yes, that is a fact! It was a bit of a disappointment to discover there would be no need for me to tweak the actual voltage available at the wire, but it sounds like my thermostat is going to do a far better job anyway!

geniescience
01-31-2007, 06:38 PM
So it is not an issue how warm the floor could become;; the upper limit is only reached when the thermostat is set to that (high) temperature. And, the thermostat being better than expected, means you don't need to simulate the thickness of a concrete installation. Combining these two pieces of information, we can come to the conclusion that an insulating underlayment is far more preferable than a CBU. It also saves you money in operating costs, but that is only half-pennies less than the pennies a day you would have spent.

david

Bob NH
02-06-2007, 06:47 AM
If you are going to heat a concrete floor, you MUST have very good insulation between the concrete and the earth. Otherwise, you will be spending a lot of money heating the earth, which is a VERY LARGE heat sink.

If you try to store heat in the thermal mass of concrete, the heat is going to be leaking out the bottom to the earth faster than it is leaking out the top to the air because conductive heat transfer rate is greater than convective heat transfer rate.

Any hard surface floor such as ceramic tile will alway feel cold to the touch unless it is as warm as your foot. That is because it is a good conductor of heat. A steel file cabinet and a carpet in a room are the same temperature. Put a hand on each and see which one feels colder. A mat that you toss on the floor to step out on will do more to keep your feet warm than heating a tiled floor.

You don't get enough "radiant" heat from a floor to give you much sensation of warming. It will barely keep your feet warm because it is in contact with them. If you want true radiant heat, you need something that is much hotter than the surroundings, such as heat lamps or those "wire wrapped around ceramic" heaters.

Leave the exhaust fan off when showering in the winter to keep you warmer when you step out of the shower and keep that good humidity in the house. Evaporation from your wet skin makes you cold. One ounce of water evaporating from your skin in one minute is taking more than one kilowatt of heat away from your body. If you want to add some heat, try a heated fog-free mirror. When I Googled "heated mirrors", most links seemed to be from the UK.

leejosepho
02-06-2007, 02:17 PM
You don't get enough "radiant" heat from a floor to give you much sensation of warming. It will barely keep your feet warm because it is in contact with them. If you want true radiant heat, you need something that is much hotter than the surroundings, such as heat lamps or those "wire wrapped around ceramic" heaters.

Some structures are heated entirely from nothing but "radiant heat" in the floor, yet I do hear what you are saying there.

If it is still cool enough for a legitimate test in a few weeks, we will see what difference our heating wire in our bathroom floor actually makes ... and at the very least, we will be standing on tile that does not suck heat from our feet as quickly as it would with nothing but mortar inside!

geniescience
02-07-2007, 06:41 AM
Bob is right about many things.

I agree with his conclusions 99.9% of the time.

We may find after a long discussion that I also might agree on the one thing that I cannot lend my support to here. Or he may have been attempting to drive home a point, and using a strongly worded conclusion to do so.

Skin temperature is always lower than body temperature.

When discussing heat transfer between two objects, we could use the strictest definition of heat which means we ignore skin temperature and always refer back to body temperature. However, people only feel heat on their skin. (More later about this. To be continued). When someone's skin temperature gets raised by a new heat source, that immediately creates a new point of reference.

So skin temperature is a moving target and that fact alone makes any discussion of "feeling heat" extremely complex. Phew! :o

Repeat: once your cold winter feet get warmed up by the tiles, they won't feel so warm anymore. The tiles I mean won't feel so warm any more.

Furthermore, the net heat transfer will still be in the opposite direction. I mean away from your body. You will be losing heat to the tiles. (More later. See below, about ocean water). Bob mentioned the rate of heat transfer; tiles are a good heat conductor. This is a crucial part of the analysis.

To complicate things even more, I'll say this: that the psychological feeling of warmth (heat) going towards/into or away/out of the body does not depend on object/skin temperatures, and also not on the rate/speed of heat loss, but on the comparable heat loss rate -- with other surfaces nearby! Comparable in one's immediate physical memory. Phew! :o Phew! :o

It is true that tile (porcelain or ceramic) will pull heat away from your skin.

It is true that tile (porcelain or ceramic) will pull heat away from your body (and thus skin), even when the tile is heated -- except initially when your feet are cold. After your feet get warmed up, the tile floor is still cooler than your body temperature. The RATE of heat flowing away from your body is much lower when the tiles are heated, and this makes the tile surface feel warm, to some, and not warm to others.

A heated tile floor, when built on an insulating underlayment like cork or synthetic membrane, will produce enough heat to feel really warm to anyone whose house is surrounded by cold radiating in from the outside. At first, your cold feet will be warmed up. Later, when your feet are warmer, the heat loss (from warmed feet to tile) will be less than the heat loss from feet to wood floor -- assuming you have a wood floor in the rest of the house. This is what I meant when I mentioned "comparable surfaces nearby".

I think a heated floor will also feel warm to anyone in a warm climate too. When direct sun is shining on it you can still notice the difference but it's no longer as significant; the sun is the strongest heat radiator we have.

A comparable phenomenon I think is this
- A.) hypothermia in warm ocean water, versus hypothermia in water that "feels cold" to start with. Staying for hours in warm water will suck heat energy out of your body.
- B.) Feeling, and enjoying feeling, warm ocean water, versus feeling water that "feels cold" to start with -- and not enjoying the sensation.

Part A.) is reality, regardless of feelings, and Part B.) is all about feelings, sensations. Both waters, warm and cold, are below body temperatre, and yes they both remove heat energy from you. One feels warm; the other feels cold. For how long does the warm ocean feel warm?? Everyone can have a different answer, since it depends on one's point of comparison.

Conclusion: three things to do: use an insulating membrane, use an insulating membrane, and use an insulating membrane. Then you will have heat so high that even the most sceptical person will appreciate the warmth. Not only will it feel warm at the first second, and the second second, and so on for many seconds, but also AFTER it warms your feet up, it will still feel warm to your senses.

Many people feel frustrated when the heated tile floor only seems to work for a short time while before it feels cold again. Their feet have gotten warmed up to a level that now causes the point-of-reference to change, and the sensation of warmth disappears. That is frustrating. The shifting point of reference.

I believe the most sensitive people are engineers who understand heat transfer. They can feel the differences in heat flow rates (heat loss or transfer), to a finer degree than anyone.

David

Bob NH
02-07-2007, 08:37 PM
You don't get enough "radiant" heat from a floor to give you much sensation of warming. It will barely keep your feet warm because it is in contact with them. If you want true radiant heat, you need something that is much hotter than the surroundings, such as heat lamps or those "wire wrapped around ceramic" heaters.


leejosepho and geniescience:

I try to use precise language. That is why I said, "You don't get enough "radiant" heat from a floor to give you much sensation of warming."

I was talking about real radiant heat. The kind that comes from thermal radiation. The kind that varies as the 4th power of the absolute temperature as represented by the Stefan-Boltzman law. The kind that gives you the sensation of warming that you get from a heat lamp, or from standing in the sun, or from a fireplace.

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. You get a sensation of warming from convection of warm air that is hotter than your skin temperature, or from conduction as when you put your hand on a hot object.

Most "radiant" floor and ceiling systems heat the air and surfaces in the room to the control (thermostat setting) temperature. But that doesn't help much when the dry air that exists in the winter heating season evaporates a lot of water from your wet skin. You can be cold in 75 degree air if you are wet and the dew point in the room is 35 degrees. At that point, you want high intensity heaters such as radiant or convective heaters operating at higher temperatures to replace that heat that is being lost by evaporation.

geniescience
02-08-2007, 05:37 AM
.... 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
02-08-2007, 07:33 AM
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
02-08-2007, 09:17 AM
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.

Rancher
02-08-2007, 02:35 PM
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
02-08-2007, 02:55 PM
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!


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
02-08-2007, 03:07 PM
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.

leejosepho
02-08-2007, 03:10 PM
I'd have to refresh my memory and research but it seems that they run about 120 degree water thru the slabs...

Yes, and I believe I read somewhere that 140 is the high limit ... maybe to avoid potential thermal damage?

jadnashua
02-08-2007, 03:58 PM
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.

sparking5
02-11-2007, 05:32 PM
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.

leejosepho
02-11-2007, 06:07 PM
... 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.

Everyone seems to at least agree heated tiles will reduce the loss of heat from bare feet.

leejosepho
02-18-2007, 06:21 AM
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!

jadnashua
02-18-2007, 02:22 PM
Screeding thinset works and is fairly inexpensive, but self-leveling concrete (slc) is faster. Check it out, then decide.

leejosepho
02-18-2007, 03:58 PM
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.

jadnashua
02-18-2007, 04:28 PM
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
02-18-2007, 06:27 PM
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

leejosepho
02-18-2007, 06:58 PM
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.


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:

jadnashua
02-18-2007, 07:18 PM
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
02-19-2007, 04:43 AM
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

leejosepho
02-19-2007, 01:26 PM
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!