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How to Install Radiant Heat on a concrete slab

Bare feet on concrete
Slab Heating System

Whether it’s summer or winter, the rooms in your home that are on a concrete slab are guaranteed to be the coldest in the house. During the winter months, these floors can even get so cold that they render the room useless. Many homeowners in this situation ask how they can solve this problem in order to get their room’s functionality back. The answer is underfloor heating.

Warming up an Existing Slab

Insulating the top surface of the slab can help take the chill off of your floors. It can even reduce your heating bills by 10 to 20 percent, according to the U.S. Department of Energy. A cork or synthetic cork underlayment is a good insulator. What’s even better is a slab insulated on top with a floor-heating system embedded in that top layer. That way, you can keep your floors cooler during the summer months and warm them up during the winter months.

Heating a New Slab

However, if you’re building a new home or putting an addition on your home, you are in a unique — and advantageous — situation. Before the concrete is poured for your basement, garage, sunroom, etc., you have the opportunity to add radiant heat to the slab. This will ensure that every room with the slab heating will be comfortable year round. But, because the heating cable is embedded within the concrete, it also gives the homeowner maximum flexibility with their flooring choices.  

When installing radiant floor heating above the subfloor or concrete slab, thinset or self leveling is applied, which essentially glues the heating element to the flooring and the subfloor or underlayment. This can be problematic because if the homeowner ever decides to replace their flooring (for instance, switching from tile to hardwood), the heating element may have to be replaced as well because it’s attached to the flooring. When you embed a floor-heating system within the concrete slab, the flooring above can be replaced without affecting the heating system below.

If you have the option to embed a WarmlyYours floor-heating cable within your concrete slab, here’s how to do it.      

Slab heat installation step 1

Step 1

Pull out your custom installation plan and identify where the thermostat should be placed. The first thing your electrician should do is install the thermostat and its junction box as well as any relay panels, if necessary. Your electrician can decide which electrical rough-in kit is appropriate for your home.

Step 2

Step 2 for installing slab heat

Using a digital ohmmeter, test the heating element’s ohm value between the two conductors (yellow and black for 120V, red and black for 240V systems) and verify that value with the value on the product’s CSA tag. Also, test the heating element with a megaohmmeter between each conductor and the yellow/green ground wire, one at a time. The 500 VDC Megaohm Meter tests for insulation resistance between the conductors and the ground and should read infinite, or OL.

Step 3

Step 3 of installing slab heating

The concrete installer should spread and tamp down at least 8 to 12 inches of crushed rock aggregate. Then, a 4- to 12-inch layer of sand should be spread evenly over the aggregate. On top of that, 2-inch polystyrene insulation (or better) must be installed. This insulation should also be placed vertically around the perimeter of the slab to prevent heat loss from the edges. Finally, heavy-gauge wire mesh or rebar should be used for reinforcement. Wire chairs or concrete pavers can be used to prop up the wire mesh or rebar.

Step 4

Step 4 of installing slab heat

Using plastic cable ties, the electrician should attach the temperature sensor and heating cable/mat to the wire mesh per your custom installation plan, being sure to avoid any overlapping, touching or crossing of heating wires. Install the sensor at the same depth and midway between the two heating wires. Once this is done, the heating cable and sensor should be tested with an ohmmeter and then inserted into a metal or other approved conduit that goes from the floor to the junction box in the wall. The sensor wire should be run to the controller in a separate conduit from the heating wire cold leads. Never run the sensor wire next to, or above or below, a heating wire. 

Step 5 of installing slab heat
Step 5

Now that the heating element and sensor are installed, the concrete installer can finish pouring the slab. The installer should pour 4 to 6 inches of concrete to bury the heating element, leaving it 2 to 3 inches beneath the finished concrete surface. Continue to test the cable with an ohmmeter during the pour. 

Step 6 of installing slab heat

Step 6

The electrician should test the heating element and sensor with an ohmmeter and megaohmmeter one more time. Be sure to enter the results on your warranty documents.

Step 7 of installing slab heat

Step 7

Once the concrete has fully cured, the electrician can complete all of the wiring for the thermostat, junction box and relay panel, if needed. Breakers should be turned on, and the system should be activated to allow the electrician to check the amp draw of the heating element. If everything is in working order, you’re done! 

For full installation instructions, please consult WarmlyYours’s Slab Heating Installation Manual. Additionally, if you have any questions or issues during installation, feel free to give the WarmlyYours technical support team a call. They are available 24/7 at 800-875-5285 for your convenience. 

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