help with ceremaic floor heating

December 22, 2004 2:52 PM

Ceramic tile floor heater question. Not hot water circulating through tubes, but a resistance heating wire in thinset mortar under the ceramic tiles. It just don't get very warm. (MI)

New addition to our house. Plywood subfloor in the new master bath. I was surfing the internet one day looking for ceramic tile floor patterns when I saw this heating system. I did a little research, and saw that most systems of this type use wires in a plastic mat that is installed in a scratch coat of thinset mortar. The ceramic tile is then installed as usual. I talked to my contractor, and he said "well, those Home Depot type systems don't have much of a warranty. I'll see what i can find." He came up with this programmable thermostat controlling this heating wire.

Everything checks out OK. No breaks in the wire (continuity test) no breaks in the sensor loop and good voltage from the circuit breaker box to the thermostat. It just don't get very hot. By not very hot i mean not at all. Using a digital instant read meat thermometer we see the air temp in the room is 68 and the floor temp is 68, even after the floor has been left on for 8 hours on the highest setting.

I haven't paid the contractor his final payment ($1,100) while I'm waiting for a resolution. He says everything is OK. I say it doesn't do anything. Are my expectations too high? The manufacturer will send a service tech to my home on January 5. Ay thoughts.

posted by fixedgear to home & garden (14 comments total)

Your expectations are not too high. Something is wrong, either with the equipment or the installation. Radiant floors don't get hot to the touch, but definitely warmer than room temp. See what the service tech guy has to say.
posted by Specklet at 3:44 PM on December 22, 2004

I was about to say that those things are meant to heat slowly, so you might not feel much by hand, but from what you described it does sound like it's doing nothing.

What you need to determine is does the thing heat the room? Since it sounds like you have a seperate thermastat for that room, leave it on overnight with the door closed and the thermastat cranked up. Does the bathroom get warmer? With the door closed your bathroom should heat up to be warmer than the rest of your house.

The other problem could be that the system just isn't big enough to make any differenence. Do you have good insulation under the heater? Maybe the heat loss through the floor is enough to offset the heat gain from the heater and the floor tends to equalize with the air temperature. You might need to do some heat transfer math to determine if your heater is undersized for the job.
posted by jacobsee at 3:47 PM on December 22, 2004

Since he's the one who picked out the system, you've got a bit more leverage, and you're definitely right to hold back on the payment till this gets resolved. If he says "Everything is OK", like "That's how it's supposed to be", when the floor's not even getting warm, then he's basically admitting he sold you system that doesn't really do anything.

On the other hand, getting the tech rep to come is a fair thing--it is definitely possible that there's something wrong that has nothing to do with the contractor, and if you can confirm whether or not it's installed right, that'd help. If he installed it OK, at your direction, and it's a faulty unit, then it's not really fair to hold him financially responsible.

One important point--it's very possible that you've chosen a tile, or he chose a thinset, that's just too good of a thermal insulator, so the heating system could be working, but the heat's not getting through very effectively. In that case, I'd say that the more he was involved in the choice of tile, the more responsible he is (especially once he knew heating elements were in the picture). If you basically told him what tile you wanted, and then said "Install a heating system under it", then it's not really fair to make him eat the cost.

One way to check that last point--do you have any spare tiles? Try putting something warm behind one. Ideally, if one of you can track down an extra section of the heating element, try hooking that up to a circuit, underneath a piece of your tile, and see what happens.
posted by LairBob at 3:52 PM on December 22, 2004

Just channeling my husband for you: he installed one of these floors for our bathroom just a month or two ago. Could the thermostat itself be defective? We found ours was. In addition to the continuity test for breaks in the wire, check resistance with an ohm meter and that will confirm whether the wire is okay - a continuity test doesn't rule out a short. Good luck!
posted by deliriouscool at 6:19 PM on December 22, 2004

Just to clarify, if you should try the resistance check: the instructions that came with the wire are likely to give a range of acceptable resistance readings. The manual for ours is written to be appropriate for several size heaters and indicates a range of 10-250 ohms. Lower than 10 ohms would point toward a short.

Another thought: could another heat source (i.e. a furnace duct) be fooling the thermostat by warming the area of the floor where the sensor is buried?
posted by deliriouscool at 6:37 PM on December 22, 2004

The thermostat was thought to be the problem, and the plan was to replace it. It seems now that the manufacturer doesn't want to do that, as they spent 45 minutes on the phone talking my builder thought the troubleshooting process for the second time. Troubleshooting also included a resistance check, but thanks anyway.

It has now been on for ~12 hours and has not raised the floor temp at all. I want the thermostat replaced, or at least checked to see that there is sufficient voltage/amperage coming out of the 'stat to the wire. I think that the sensor loop may be installed incorrectly (too close to or even touching the heating wire) and as a result is just turning off the thermostat too soon.

Pictures here,
here, and here.
posted by fixedgear at 3:18 AM on December 23, 2004

Your links want a password.
posted by luser at 3:44 AM on December 23, 2004

you could try forcing the thermostat on and seeing if the temperature then increases. this has the risk of damaging something though. (you'd force it on by either opening it up if it's semi-mechanical, and shorting something out or, if it uses a sensor, replacing the sensor with some fixed resistance, i would guess).
posted by andrew cooke at 4:35 AM on December 23, 2004

Sorry, that should be pic,pic, and pic.

Andrew:

If it were a self-install I would try to do that - replace the sensor with some fixed resistance and fool the 'stat into turning on. Since I'm paying someone else I guess I'll wait for that tech to get here, since it looks like my builder missed something.
posted by fixedgear at 4:54 AM on December 23, 2004

sure, good luck. incidentally, is this low voltage?!
posted by andrew cooke at 5:17 AM on December 23, 2004

No, the system is 110 volts.
posted by fixedgear at 5:59 AM on December 23, 2004

ok (i wondered because the only thing comparable we have - for heating the bed - is 12V, but the resistance you gave didn't make sense...)
posted by andrew cooke at 6:16 AM on December 23, 2004

thanks for the pictures...sounds like you are on the right track. just curious...do you know why are the loops are spaced closer together in the top row?
posted by jacobsee at 9:27 AM on December 23, 2004

The loops were concentrated in front of the tub and shower, spread farther apart near the toilet, and not run at all under the vanity. this was one of the supposed advantages of using the wire vs. the mat, the ability to concentrate the heat where it did the most good.
posted by fixedgear at 10:29 AM on December 23, 2004