Radiant heat: temperature of the floor

elk2000November 9, 2012

Been doing a lot of research for heated floor to install in our current small bath remodel (2nd floor). The installation we pretty much agreed on is:

a. Cerazorb or other insulating cork.

b. RPM mats (do I need to staple it to cork?)

c. Floor heating wires (2" spacing); 2 sensors

d. SLC over wires

e. Thinset / porcelain tiles / grout

Sounds right?

Few questions:

1. We currently don't have 240v line, but can get it from the basement. How important this is in heating: does the floor warms up faster / warmer? Should we even bother?

2. Been considering Suntouch Warmwires and Warming Systems wires. With 2" spacing Warmwire produces 15w/square foot, Warming Systems - 12w/square foot. Also Warming Systems says that max temperature is 90 degrees with good insulation. Can't find same info for Warmwires. Does the voltage (120 v 240) play a role in how warm the floor is? What is the max temperature I can get realistically?

3. The room is 8'x5'. 3'x5' of that will be shower with Kohler cast iron pan. Do we need to install cork / RPM mats / SLC (but no wires) under shower pan to make floor equally even? If not, what do we install under shower pan to bring the floor to the same height with the rest of the room? Does it need to be same height?

Thank you

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Others will answer with more detailed information.

I have Warmwire by Suntouch installed in my new bath. I did it myself and the electrician wired it for 240, the Warmwire product is selected for either 110 or 240. Electrician said that 240 was better, I think it warms up faster. All should warm up to what ever temp you set it at.
Wires installed:

then with the plastic lathe I used over the wires:

SLC being poured:

With regard to the shower pan, I was told that I could place my tub onto the underlayment before the SLC. But I wanted the tub to be on top of the SLC so that is what I did. I did not run my wires under the tub, and kept 6 or 8" away from the toilet cutout.

What are RPM mats?

I notice that you do not have a de-coupleing membrane in your plan. Ditra is one. It allows a bit of horizontal movement to happen without cracking the tile. It is set on top of the SLC with thinset, then the tile is set with thinset.

    Bookmark   November 9, 2012 at 3:56PM
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I really like your idea for plastic lathe. Less chance to break the wire :-)

RPM mat is an alternative to backerboard with built-in grid for heat wire installation. From what I've read it simplifies whole floor / wires installation significantly. Even though it's more expensive than backerboard (about $14 per 20"x44"), I think the higher price is justified. Plus the room is small, so we don't need a lot.

As for Ditra, we haven't decided yet whether we will put it in though we have plenty left from kitchen tile installation. I'm afraid it will raise the floor more than we can allow it. I also read somewhere that having Ditra between wires and tiles results in slower tile warming up and temperature doesn't get as high as without Ditra. Thus the hesitation.

Here is a link that might be useful: RPM mats

    Bookmark   November 9, 2012 at 4:26PM
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Those mats look nice. On my installation I put the lathe on top of the wires. I was careful and there was no wire breakage. The lathe is to add strength to the SLC sort of like how when concrete is poured it is re-enforced with screen or re-bar.

    Bookmark   November 9, 2012 at 4:40PM
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