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algee 01-26-2011 06:23 PM

Radiant Floor Heat Mat
I had a Danfoss LX 5' radiant floor heat mat installed under a tile floor in my bathroom remodel. The contractor who did the install did not take any ohm readings before or after the install so I can't register the warranty. Does anyone have any suggestions for me? Also, the floor gets warm, but not evenly. Would the floor be cooler by the outside wall? I thought maybe the sensor was put towards the inside and may not register the temp accurately across the entire floor. Thoughts anyone?

Daniel Holzman 01-26-2011 09:48 PM

The sensor only measures temperature at a single location. If the sensor reading is lower than the thermostat temperature, the mat turns on. So far as I know, all mats run on/off, I have never seen a variable voltage mat.

If the mat is on, the entire mat is on, because the current flow through the wire is identical at all points. Heat is generated because the wire has resistance, and the flow of the current generates heat in the wire. All the mat systems I have seen have uniform resistance wire, so the heat generated per foot of wire should be identical.

You apparently have cold spots, which could be due either to defective wire (non-uniform resistance), or possibly variably spaced wire, which would be an installation problem. The objective of the installation is to provide the same number of feet of wire per square foot of floor, thereby providing the same heat per square foot everywhere.

As for the resistance, the normal plan is to measure the resistance prior to installation, and check that against the resistance shown on the factory carton to make sure the wire is in spec. Then the resistance gets measured again after installation to make sure the wire was not damaged. Since the resistance was not measured prior to installation, it would be impossible to compare post installation resistance to pre-installation resistance, although if you have the original box or manufacturer's receipt, you should be able to check the design resistance for the wire. If you can get access to the two leads, you can check the resistance of the wire in place, and if it matches the manufacturer's rating within the specified percentage you are good.

12penny 01-27-2011 08:39 AM

algee....everything Daniel told you is correct. I might add ...the wire only radiates heat outward about two inches. Thats why the wire is woven into the mat with a 4" space between them. If the mat is too small for the room, then yes, you will have cold spots.

warmsmeallup 01-27-2011 09:02 AM

Based on what you've said, if the floor is getting warm in some areas but not others, there is nothing wrong with the mat. He just didn't run the element where there's no heat. It's not uncommon to cover the majority of the walk path and leave it 6" from the wall since no one stands there. If you have more than that, you may have purchased too small a mat and he covered what he could with it.

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