How to Install Radiant Floor Heating Systems

In this house, an electrician has already created a dedicated circuit for the radiant floors. Preparation is key here. Next, measure the square footage of the bathroom and order the correct heating cable length.

Before beginning installation, it's important to test all of the electrical lines and cables. This test will take place twice, before installation and after tiling. A fault sensor will sound the alarm if needed along the way.

First, test the conductor resistance with a multimeter and alligator clips. Clip one alligator clip to each of the heating cable power leads. The ohm readings should fall within 10% above or 5% below the factory reading. Record this reading in the installation manual. Now check the ground on this cable. Leave one cable connected and attach the other alligator clip to the ground braid.

If the test is successful, you'll see an O, which means overload on the multimeter. Depending on the meter model, you may alternatively see I for infinity. Now look for any small breaks in the cable. Set the meter to 1,000 volts and connect to one of the power leads and the ground braid. An O reading shows the resistance is greater than 1 giga ohm and the cable is good to go.

The sensor probe will deliver floor temperature readings to the thermostat. There are two of them. Strip the ends of the temperature probe cables. Test this by attaching the alligator clips to the sensor leads and adjust the multimeter back to ohms. The reading should fall between 8 and 12 ohms. Record in the log.

Next, it’s time to install the membrane, which will guide the radiant heating cables under the bathroom tiles. If the membrane arrives in a roll and is looking wavy, back roll to help straighten it out. Given this bathroom's small footprint, individual sheets will make the installation more manageable. A longer membrane roll is a great idea in a larger space.

The dry fit is key. Place the first membrane sheet along one edge of the room. Line up another sheet next to the first, making sure that the membrane studs line up in straight rows. This will ensure the heating cables run up and down the rows in continuous straight lines. Trim sheets to size across the ribs using a straight edge and a utility knife.

Mark the subfloor along the edge of each membrane throughout the dry fit process. Labeling both the subfloor and membrane will ensure all those dry fit pieces stick where they're meant to be stuck. Use the utility knife for cutting openings like the floor vent and toilet piping. Remove the dry fit membranes and sweep the floor to remove any dust or debris. This step is crucial for proper adhesion, allowing the membranes to lie flat.

Many radiant floor kits require using thin set to adhere the membrane to the floor, but this peel-and-stick method is faster and easier. It has the same benefit as other kits like uncoupling, which prevents any cracks due to natural movement between the subfloor and tiles. This membrane also provides waterproofing which is key for a bathroom.

Remove the clear plastic lining from the bottom side of the membrane. That fleece side will be sticky. Apply directly to the subfloor. Starting on one end, gently guide the membrane into place, smoothing it with your hands. Continue with the next membrane sheet, ensuring that the studs are lined up. You should be all set after the dry fit, but double check before the sticky layer adheres to the floor. Continue laying the membrane until the bathroom floor is covered.

Running a float across the floor is another way to ensure full contact between the membrane and the subfloor. Foam insulation creates a solid barrier along the wall and floor vent, which will keep the self-leveler exactly where it needs to be when applied later.

Before laying any cables, create buffer zones around fixtures such as the toilet. You’ll need a minimum of 2 inches from walls and fixed cabinets, 4 inches from forced air heating vents and 7 inches from center of the toilet drain.

It's time to install the cables into the studded membrane. Set the cold lead and temperature probe cabling next to where the thermostat will be installed. Remember, an electrician should connect all household wiring. In a small space like this bathroom, a 333 heated cable layout works well. The cables will heat the floor and the room.

Attach the cold lead end cables to the fault sensor. This sensor monitors the hot, neutral and ground wires throughout installation. It'll begin to flash and make noise if the wire is pinched as it's wrapped around the studs. It's time to lay the line.

Embed the heating cables between studs and weave through the space, maintaining that three stud separation. Snap the cable into the membrane, ensuring the cable fits snugly between the studs. This will help to prevent any nicks later on when topping with mortar and tile. Continue weaving and wrapping around the bathroom until the floor area is covered.

Run the temperature probe about 2 feet from the wall along one of the stud valleys between and not overlapping any cables. The sensor should be at least 6 inches into the heated zone, but not too close to a wall, air vent, or plumbing. Use a utility knife to cut away a spot for the end of the cold lead. The cable must be flush with the membrane. Use a glue gun to adhere the cold lead splice to the floor.

Now that the membrane, heating cables, and sensor have been installed and tested, pouring a leveler will help keep everything in place. It’ll also help to prevent any nicks or dings throughout the tiling process.

Combine the self-leveler and water in a 5-gallon bucket and mix with a ribbon attachment. Think pourable, but not too watery – similar to smoothie consistency. Pour self-leveler starting at one side of the room and working your way out. Spread with the float barely covering the floor membrane and cables. Smooth the self-leveler over the floors, helping it reach the walls and corners. Make sure the heating element is fully encapsulated. The goal is to protect that cable. The leveler will need to dry overnight before tiling.

Trim the excess foam insulation with a utility knife. If the knife doesn’t work, an oscillating tool can make things easier. Ceramic and porcelain tile are great choices for radiant floors as they're both durable and great at conducting heat. Avoid installing solid hardwood flooring over a heating system.

Mix up a batch of mortar. This material will be thicker than the self-leveler– similar to peanut butter consistency. Scoop a line of thin set along the edge of the room and spread with a trowel horizontally and then vertically, creating parallel even lines. Start laying the tiles at one end of the room and work your way out. See our step-by-step instructions on how to tile floors.

Once everything is cured, touch up and reinstall the baseboards. Finally, have an electrician install the thermostat for the radiant flooring system. Be sure to consult the manufacturer's instructions to see how long to wait after installation before using the system. The one we chose recommends waiting 7 days after grouting before consistent use.