How to Install Heating Under Tile

Written by angel coswell
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How to Install Heating Under Tile
Tired of stepping on a cold tile floor? You can install your own floor heating system. (girls image by Vasiliy Koval from

Floors above unheated spaces can be cold, even when heavily insulated. A floor warming system is fairly easy to install and provides warmth and comfort to the place that feels the coldest, the feet. Floor-warming systems are designed to heat ceramic-tiled floors and consist of thin mats containing electric resistance wires that heat up when they are energised, a thermostat control, and the timer. These mats are connected to a GFCI breaker circuit, which is wired into the thermostat and time controls.

Skill level:

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Things you need

  • GFCI circuit
  • Heating mats
  • Multi-tester
  • 2 1/2-by-4-inch double-gang electric box
  • Single-gang electric box
  • Drill
  • Chisel
  • Plumb bob
  • Two ½-inch diameter thin wall conduits
  • 12-gauge NM cable
  • Cable clamps
  • Set screw fittings
  • Double-sided tape
  • Grinder
  • Hot glue gun
  • Steel fish pipe
  • Vacuum
  • Chalk
  • Electrical tape
  • Heat-resistant tile
  • Thinset mortar
  • Notched towel
  • Drywall
  • Thermostat and timer
  • Wire connectors

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  1. 1

    Test and inspect your heat mat for damaged or frayed and corroded wires. Do not use the mat if you find any. Use a multi-tester to check the ohms value of each heating mat. Ensure your readings are within the manufacturer's factory-tested range of readings. If the readings do not match, your mat is damaged and must be replaced.

  2. 2

    Remove all wall and floor surfaces, including the drywall, until the framing and subfloor are exposed in the area in which you are working. The heating mat can be installed on concrete flooring or on well-insulated subfloor.

  3. 3

    Secure the 2 1/2-by-4-inch double-gang electric box for the thermostat to a secure and accessible location, using an appropriate-sized screw and a power drill. Attach the thermostat box to the wooden stud closest to the location of the heating mat 60 inches from the floor. Make sure the power leads from the heating mats will reach the electric box. Attach the single-gang electric box for the timer to the other side of the same stud.

  4. 4

    Drill a 1/2-inch hole through the top of the thermostat electric box and through the top of the timer box. Clean up the holes with a chisel so you will have a smooth surface to work with. Drill a 5/8-inch hole in the same stud you attached your boxes at about 12 inches above the boxes. Use a plumb bob to mark and drill out two 1/2-inch holes in the wooden frame directly below the two knockout portions in the thermostat box.

  5. 5

    Cut out two ½-inch wall electrical conduits to fit the length between the thermostat box and the wood frame directly below the box. Insert each conduit into one of the ½-inch holes drilled into the wood frame below the box. Attach the other end of the two conduits to the thermostat box, using set screw fittings.

  6. 6

    Run a 12-gauge NM electric cable from the service panel and through the bottom of the timer box. Pull about 8 inches of the cable through the hole in the box and attach the cable to the box, using a cable clamp.

  7. 7

    Run a short cable through the 5/8-inch hole in the stud. Push one end of the cable through the ½-inch hole in the top of the timer box, pulling about 8 inches through. Run the other end of the cable into the ½-inch hole in the top of the timer box and pull about 8 inches of the cable through, creating a smooth curve in the cable. Attach the cables to the boxes, using cable clamps.

  8. 8

    Clean and vacuum the floor. Draw out the reference lines you will use for your tiling project, using the chalk.

  9. 9

    Place and smooth out the heating mats on the floor 3 inches to 6 inches away from the wall or other fixtures with the power leads facing closest to the boxes. Ensure the mats do not overlap each other. The heating wires in one mat should be about 2 inches from the wires in the second mat. Make sure the power leads reach the thermostat. Secure the mats to the floor, using pieces of double-sided tape, ensuring the mats are wrinkle-free.

  10. 10

    Create a 1/8-inch groove in the floor, using a grinder or chisel and hammer, so that the cording of the heating mats can lay in the groove as you run it to the leads. The cording is too thick and will leave an uneven texture for laying tile if you do not create a groove. Clean out the groove and secure the cording into the groove, using a hot glue gun.

  11. 11

    Thread a steel fish tape down one of the conduits and attach the ends of the mat's power leads to the fish tape, using electrical tape. Pull the cords up through the conduit so 8 inches show and secure the wires to the box, using cable clamps

  12. 12

    Thread the heat sensor through the second conduit from the box to the floor and weave it 9 inches into the closest heat mat between two blue resistance wires. Secure it in place, using the hot glue gun. Retest the resistance of each heating mat, using the multi-tester, to ensure no damage occurred during installation.

  13. 13

    Install the ceramic or heat-resistant floor tile, using thinset mortar as an adhesive. Carefully spread out the mortar over the floor and heat mats, using a square-notched trowel. Periodically check the resistance of the mats to ensure the mats do not get damaged during the process. Replace any damaged mats. Allow the mortar to cure.

  14. 14

    Install the thermostat and timer adaptor covers to the electric boxes and patch up the wall opening with drywall. Finish the wiring connections for the thermostat and timer, following the manufacturer's instructions. Attach the sensor wire to the thermostat set screw connection. Mount the thermostat and timer and complete the circuit connection at the service panel. Test the system once everything is installed to ensure the heating system works.

Tips and warnings

  • Check to ensure the GFCI breaker circuit you are going to install the mats on has an adequate amperage. Electrical service required for a floor warming system is based on the size of the system. A smaller system can be connected to an existing GFCI circuit. A large installation will need a dedicated circuit.
  • For installations of three or more heating mats, use a ¾-inch conduit instead of the ½-inch one.
  • While installing the mats do not drop anything heavy on the mats and avoid stepping on them. Lay a thin piece of plywood over them to avoid stepping directly on them.
  • Do not install the mats on walls, under cabinets or other objects, in closets or other small areas. Do not allow any of the mats to overlap. Heat can build up quickly, which can damage the mats or cause a fire.
  • Do not cut the mats to make them smaller.
  • Be careful while working with electricity. Electrical shock could occur.

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