wiring radiant floor

aussie-rooSeptember 16, 2010

Just installed 120v radiant heat pads under wood floor, ran the wires and sensor wire up the wall to an existing thermostat control box. The existing control box controlled a 240v radiant ceiling which we deleted to install recess lighting. The problem I am facing is the power feed I wanted to use is 240v but the new thermostat and radiant floor require 120v. How do I go about change the 240v feed to 120v, it would be nice to run new romax but it would be fine to also use the existing wires and delete the double pole breaker.

Another idea I have is, directly under the thermostat location is a 120v outlet, can I tap into the outlet to get the power or is that a no no. The thermostat has a built-in gfci

It would of be nice to know it was 240v before I place the order for the radiant floor, could order 240v pads. To late now floor is down and it is not coming up.

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Ron Natalie

This is not a problem most likely. If the wire is of sufficient size for the amperage of the floor pads and this is the only thing on the branch circuit (most likely it is), then all you need to do is replace the breaker with a single pole one of appropriate rating (yes, you can probably just use one side of the double pole, but you may wish a small rated breaker anyhow). Take the other wire and connect it to the neutral bus. Please remark both ends of the wire you move to neutral WHITE.

    Bookmark   September 16, 2010 at 8:57AM
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The sticking point is going to be the sizing on the wire feeding the existing controller. Depending on the size and configuration, radiant floor heating can draw a pretty large current. The wire needs to be large enough to handle that current and not overheat. This is a safety concern, so you need to be sure you are using the right wire and the right breaker.

Typically the installation instructions for a radiant floor will say "requires a x amp dedicated circuit". Even if it doesn't, I would not want to tie a radiant floor into a regular bathroom circuit. The first time someone tried to blowdry their hair while the floor was on, it would likely trip the breaker.

    Bookmark   September 21, 2010 at 9:06AM
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Ron Natalie

I already warned him to check the rating. However, these things even for the largest sized rooms rarely go over 2000 watts. The ones typically sold for bathroom are down around 300.

    Bookmark   September 22, 2010 at 8:37AM
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