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Install your own under-floor loose wire
Electric Radiant Heat System

This article courtesy

Here is an overview on how to install your own under-floor loose wire radiant heating system.  This type of heating system is a great supplement to your whole-house heating system.  Or do you have a "cold room"... a space that never seems to warm up enough?  Or do you want to install tile on your kitchen or bath floor but are concerned that it will be cold in the winter?  An under-floor system can keep these areas warmer at a lower cost and greater comfort than any other type of heating unit!

1) Take measurements and plan wiring locations carefully

Any type of installation requires figuring out exactly how much material you will need to do the job.  It is no different with an under-floor heating project.  As noted in the diagram below, you will first need to measure the area you want to heat, excluding any furniture or fittings so that you purchase the right amount of product for your project. 

It is important to avoid placing the radiant heating wire underneath areas where you plan to install fixed furniture, such as cabinets.  You can place the heating wire close to toe kicks or the shower/tub enclosure, but leave a little room around toilet drains (so it isn't underneath the toilet) and walls are needed.

2) Decide where to install your thermostat...

The thermostat is the "heart" of your radiant heating system, controlling the power to the heating wires and also regulating the temperature of the floor.  All wiring for your radiant heating system either runs to it or from it.  Most people will install their thermostat near the entryway of the room they are heating, near the light switches.  However, anywhere you install it is fine as long as the area is dry and unobstructed. 

In some cases, the location may need to be based on the layout of your home and the location of the main circuit board.  Consult an electrician if you need assistance with the specifics.  Of course, any electrician would be glad to do the final wiring for your project!  (If you're interested in seeing what a state-of-the-art floor heating thermostat looks like, Warmup offers an excitingnew energy efficient, programmable floor heating thermostat called the 3IE.  See pictures below.)

 Floor heating thermostats usually require a double-gang box with two 1/2" conduits down to the floor level... one for the heating wire and one for the sensor wire.

3) Insulate your floor beneath the heating wires for increased efficiency!

We recommend using our insulation boards when installing over concrete slabs. Warmup Insulation Boards will save you money when used in conjunction with underfloor heating by acting as a very efficient thermal barrier. They reflects the heat upwards into the floor tile instead of allowing heat to warm up the concrete slab below. By using Warmup Insulation Boards you will find that after switching on your heating, your floor tiles will warm up in about 10-15 minutes. Without insulation boards it could take anything from 2-3 hours, or more.

When installing insulation boards, determine how many you need based on the measurements of the area you are heating.  Each board is 2' x 4' x 1/4" and can easily be cut with a utility knife to allow for placement in every nook & cranny.  You will apply a construction adhesive to the subfloor and place your boards on top.  Over plywood sub-floors, you will add provided screws every 8 to 12 inches for added bonding.  Due to the thinness of our boards, you can have the benefits of insulation without interfering with your design plans!             

4) Testing makes perfect... be sure your wires are not damaged before, during or after installation! 

You should get a multimeter or ohmmeter to test the resistance of the wires.  This should be done before, during and after you lay down your wires, prior to installing the actual flooring.  The reading you should get for each type of wire system (120V or 240V) is provided in the included installation manual. These testing meters are about $20 at your hardware store or available from Warmup.

5) Laying down the wire...

 Start at the thermostat and route the power cable or "lead wire" into the conduit. From here, lay down your heating wire in loops at 2", 3" or 4" spacing with the provided tape. 

1) For MORE HEAT or to compensate for a cold subfloor, use a 2-inch spacing between wires, giving you the highest heat production.  

2) At 4" spacing, you will have less output, but it is the recommended spacing over Warmup Insulation Boards as you do not lose heat downwards and therefore require less wire for great results.

When ordering your loose wire system, review the manufacturer charts which will give you the square footage you can achieve at various spacing. Advanced users even alternate the spacing within a same room, with more heat at the vanity, and less heat in the walking closet for example.  

Here are some pictures of a typical installation pattern.  Note that the wire is held in place with tape (supplied by the manufacturer), not staples or other mechanical fasteners that may can cause shorts and/or damage the wires.  The first graphic shows the layout with small pieces of tape holding the wires in place.  The second graphic (below) shows the entire length of wire being affixed to the floor with tape.  This is important so the wires do not become displaced with applying the thinset over the top.

Warmup's wires are only 1/8" thick, and do not raise your floor levels by more than 3/16" when coated with self-leveler or thinset.. the minimum recommended thickness of thinset.  As thin as they are, Warmup's wires provide the fastest heat up times in the industry and are made with advanced, commercial grade polymers that have the strength and durability to last longer than traditional PVC wires. Note:  Warmup wires can be applied with cable straps or "clips", but often only require the provided tape, in order to maintain the floor profile as low as possible. 

Installing the floor probe...

The purpose of the floor probe is to monitor the temperature of the floor.  Remember that the thermostat reads the air temperature, not the floor temperature.  There may be a circumstance where the room may become warm (such as a sunny day) but you still want the floor to stay warm.  The floor probe allows some control over the floor temperature independent or in concert with the thermostat.

Install the floor probe or "sensor wire" by routing it into the second conduit to the thermostat box. Lay the sensing tip of the probe into the heated area. Make sure not to overlap or cross over any heating wires, and keep it centered between the nearest wires for accurate readings.

Depending on the thickness of the probe, you may want to chisel a channel into the floor (or insulated panel) so it lays beneath the level of the heating wires.  It should be taped in place, as were the wires.

Protect the wire with a thinset mortar coating...

Using a flat trowel, cover your wiring system completely with either a floor leveler or a modified thinset.  In this example the contractor is using a polymer-modified thinset mortar. (We often use MAPEI FLEX or CBP Versabond for our installations.) You can reduce that layer to a strict minimum, but it will provide for an easier tile job. In any event, you must always make sure that the wires are completely imbedded in these compounds so as not to be exposed to the air and over-heat. Do not attempt to set tile into this protective coat! 

After it has cured (a few hours to overnight depending on thickness and the manufacturer's suggestions), start laying down the tiles or other flooring) as normal. 

Important:  Do not activate your radiant floor heating system until the cementitious materials are fully cured.  This will be determined by your floor installer or by reading the manufacturer's instructions. As a rule of thumb, we recommend 3 to 7 days wait time.

Watch this instructional video!

Here is a video of an actual installation job in a small bathroom with Regis and Mike of Warmup.  This will give you a realistic view of the taping of the wire and the coating with a floor leveling compound.

We have a helpful FAQ page on our website that will answer additional questions you might have.  Once you visit, you will also be able to view all of our product offerings along with installation pics and helpful step by step videos. Our experienced staff at Warmup is always on hand to answer your radiant floor heating questions.  You can visit us at and fill out a no obligation "quick quote" to see how we can help, or just give us a call toll-free at 1-888-927-6333.

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