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TommyC 03-02-2012 06:34 PM

Floor Heating?
 
We'll be remodeling a bathroom soon. We'll probably do a tile floor and we are thinking that a little floor heating would make that tile floor a lot more comfortable on bare feet. I'm guessing that the only option we should consider is electric - we don't have any other in-floor heat in the house and this is a very small bathroom. Some questions:
Does anyone have experience they would like to share?
Any "gotchas" I should look out for?
If I only care about warming the floor and I don't care whether I get more heat in the room, are there any lower-cost options that might be appropriate?
I'd love some feedback. Thanks! :thumbup:

Daniel Holzman 03-02-2012 07:40 PM

Electric heat works nicely. Do a search on this forum, you will find many posts. I installed mat heating under my kitchen tile, I like it a lot, but no mat radiant system is going to warm your house, so you are not going to save any money by getting a lower power system, most of them are about 10-15 watts per square foot. Installation is a bit of an advanced DIY job, since you have to wire it, then install the tile, but if you are good with wiring and tiling, you can't beat the feeling of a warm floor.

warmsmeallup 03-04-2012 03:46 PM

Look for warranty (10 years minimum) and be sure to get a GFCI Thermostat to control it. Higher watt output, higher running cost. Lower watt output, lower running costs, however, the higher the wattage psf, the faster it will recoup. If you get a lower wattage (8-10 watts psf) it will be on longer to come up to temp. So, bottom line, they will cost the same to do the job you want them to do so you're better off with the higher watt product.

pgc555 03-04-2012 08:17 PM

Tommy,
Do you have a floor heat company chosen yet? I have installed many
brands mat or cable.

Yoyizit 03-04-2012 08:40 PM

Is there any other floor covering for bathrooms that is easy to remove for when your electric heat element opens?
Also, what is the expected lifetime for this kind of heating when installed by an installer of average skill?

pgc555 03-05-2012 07:32 AM

Not sure what you mean by "when heat element opens?"
Floor heat ,once installed in SLU it's done! No moving parts to wear out.
WarmlyYours is a sponsor at the bottom of the page and makes a fine system.

Yoyizit 03-06-2012 10:40 AM

Quote:

Originally Posted by pgc555 (Post 870792)
Not sure what you mean by "when heat element opens?"
Floor heat ,once installed in SLU it's done! No moving parts to wear out.
WarmlyYours is a sponsor at the bottom of the page and makes a fine system.

Actually the parts do move due to thermal expansion and contraction and so eventually fail probably due to metal fatigue.
Maybe some university has published a report on the MTBF for floor heating systems.

pgc555 03-06-2012 05:37 PM

"Actually the parts do move due to thermal expansion and contraction and so eventually fail probably due to metal fatigue."I disagree. Maybe some of the floor heating companies will chime in on this point.

pgc555 03-06-2012 05:40 PM

Quote:

Originally Posted by Yoyizit (Post 871829)
Actually the parts do move due to thermal expansion and contraction and so eventually fail probably due to metal fatigue.
Maybe some university has published a report on the MTBF for floor heating systems.

I disagree. Maybe some of the floor heating companies will chime in on this point.

JetSwet 03-06-2012 06:16 PM

The heating membrane doesn't move if that what is being talked about? It's low voltage wires morter, thinset safe and won't affect the subfloor ply underneath.

Yoyizit 03-07-2012 05:36 PM

Depends on what material the pipes or wires are made of.
http://en.wikipedia.org/wiki/Invar

I think the tradeoff is toasty warm floors for a long time vs. tearing up the floor after 5 or 10 years when the heating element or pipe fails, but if bathrooms are remodeled every 10 years due to fashion then the heating only has to last about this long.

warmsmeallup 03-07-2012 06:16 PM

A low voltage element will last 25 years, minimum. In fact, it's their non-prorated warranty. It's not at all the same element as the line voltage systems use. Since it's a single copper stranded wire, there is no "fatigue" to speak of.

Daniel Holzman 03-07-2012 08:27 PM

The fatigue being discussed is the potential fatigue due to the copper wire changing length as it warms (lengthens) and cools (shortens). If the wire is sufficiently well bonded to the thinset, the wire actually does not change length, however it exerts stress on the surrounding mortar in accordance with Hookes law, and of course the mortar causes the wire to become stressed. This is the same type of stress exerted on concrete by reinforcing bars changing length due to temperature change. Stress changes are actually what causes fatigue, curiously if the wire were not bonded to the mortar at all it would not fatigue, since there would be no stress on the wire as it changed length.

Depending on how your thermostat is set, you could easily have two stress cycles per day. This would lead to several hundred cycles per year, which is what fatigue is all about, multiple cycles of stress, induced either by direct tension, temperature change, or deformation.

All that said, copper is relatively fatigue resistant, meaning it typically can handle more than 10,000 cycles without significant reduction in strength. This is a minimum of 20 years in the floor, and even after this period of time, the copper still retains at least half its original strength. So relax, have another beer. Floor failure is almost certainly more likely due to improper installation, which of course could never happen in a DIY setting, thermostat failure, or tile failure leading to exposure of the wire.

By the way, this is quite different than the effect of strain hardening on copper, which you typically see when you cold work copper, for example when bending copper flashing. In that case, you stress the copper so much that it actually strain hardens, making it very brittle if you bend it back and forth too many times. This is a totally different phenomenom than the small deformations due to heating a wire, since in the case of flashing you are radically deforming the copper (think 90 degree bend). Same thing happens when you try to bend a copper pipe, it actually gets harder to bend (but easier to break) each time you bend it.

warmsmeallup 03-08-2012 08:14 AM

Yeah, like I said..no fatigue "to speak of"...:wink:

Kukka 03-08-2012 08:07 PM

Under floor heating
 
I had heating pads installed under my bathroom floor for a year now.. It is really great. I bought two electric rolls/pads from homedepot at 170 each, and that were enough for my standard 5x7 bathroom. the warranty of the heating roll is for 25 years.

You may want a programmable thermostat. I forgot how much I paid for it, but it is really worth it because it takes more than 30 minutes for the floor to heat up to the preset temperature.


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