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Hop while shaving!

Richard Moore

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Really nice remodel of a 1901 house today. Probably the cleanest old home I've done. However...one strange thing was one of the bathroom floors. I'm familiar with newer electric, under-tile heating (recently installed a bunch myself) with a temperature sensor embedded in the thin-set and a specially designed "floor-stat". The recommended comfort range for those is 80-85F.

This bathroom had a normal "air" thermostat controlling the floor. It would click on and off around 68F (the ambient temperature of the house - bathroom door open), but look at the floor readings.

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It was a bit uncomfortable in socks and I can't imaging standing still long enough in bare feet to shave. I told my client that I consider this to be abnormal and in need of modification (read...ripped up and start again). This one is going to be a major bidding war, so it's very likely I won't actually have to write it up. In the meanwhile...comments anyone? Was this ever a normal way to install under-tile heat?

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Did someone make it up as they went along? They must've....

You have to have the floor temperature control; you can't set floor temp w/a wall thermostat because it gets too dang hot (as we can see!).

Basic fundamental of radiant heating design; it's not about the temperature of the air, it's about temp of surfaces, and understanding the physiology of human comfort. A properly designed and functioning radiant floor heating system won't feel hot; at least, it shouldn't.

Robert Bean just provided an illuminating explanation of this over @ Mike's "other" gig @ JLC Online; do a search & read it. It explained a lot of stuff I never understood very well.

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Hey Guys,

Thank you hery much. I am presently reconstructing a condo on Madison Avenue in Manhattan. I am having such a system installed. The electrician that is installing the system is wiring it up with a wall stat. I just called my client and educated him about this problem.

There is going to be a design change.

Thank you.

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Just to clear things a little. The "floor-stat" is a fairly regular looking wall mounted thermostat but has an input for a lead to the embedded sensor as well as the power leads. I'm not sure how much of the install your electrician is doing but it would be normal to run the 240 (maybe 120) power to a wall box. The actual installer (tile guy, whatever) would then run the wires from the radiant mat and sensor back to the box.

One tip. The sensors are cheap and it's a real good idea to embed a second one a short distance from the first, with the wire also to the box. Then, if anything goes wrong with the first sensor you can simply change the leads and don't have to rip up the tile.

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Here's a couple of pre-tile photos of mine.

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In the first you can see the various leads at the wall box. In the second, the two sensors are to the left.

I used a product called SunTouch and read the manual very carefully. It's a "good read" for most installations. Find it here...


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