The gentle warmth of electric radiant floors is always welcome underfoot on a chilly day. Radiant floor heating is so effective because it generates heat from electric cables and radiates that heat to solid, dense objects. These objects—subfloor, thinset mortar, and tile—help to evenly spread out the heat and to retain that heat for a long time.
For just a few cents a day, you can keep your flooring warm and toasty. Your radiant heated floor can even be a supplementary room heating source.
Make sure that the floor is capable of properly supporting a grouted tile floor. Floors that have too much deflection, or bounce, will result in cracked tiles and grout and possibly broken wires.
Installing Electric Radiant Floor Heating
Electric radiant floor heating systems are built from electric cables that are run back and forth between cable spacers. After the entire system is laid and tested, a wet tile mortar called thinset is troweled directly over the cables, with tile placed on top and then grouted.
The cables are spaced around 3 or 4 inches apart from each other. Long plastic strips of plastic called cable spacers act as the end points for the cables. Attached to the subfloor, the cable spacers act both as secure anchors for the cable and as devices that maintain proper cable space.
Electric Floor Heating Mat Systems
A similar type of radiant floor heating is a mat system, where the cables are already spaced and attached to a flexible mat. The mat system is easy to install and works well for simple spaces with few angles. However, the cable-and-spacer system (this project) offers greater flexibility and is less expensive.
When to Install Electric Radiant Floors
Installing electric radiant floors must be done after the subfloor has been installed and before the tile has been installed. Radiant heating systems' cables are permanently embedded in the wet thinset mortar. The tile is then laid on top of the thinset mortar.
Hire a licensed electrician to bring electricity to the start point of the cable run, to install the thermostat, and to make all of the splices. All work must be done in accordance with the National Electrical Code (NEC) and local building and electrical codes.
Equipment / Tools
- Hot glue gun
- Chalk snap line
- Cordless drill
- Tape measure
- Square-notch trowel
- Floor heating cables
- Floor heating cable straps
- Radiant heating underlayment
- Electric floor heating thermostat
- Cement backer board
- Industrial-grade hot glue
- High-temperature tape
- Thinset mortar
Add Cement Backer Board
With the cordless drill, drive screws through the cement backer board and into the subfloor.
Lay Radiant Heating Underlayment
With the square-notch trowel, trowel thinset mortar onto the subfloor. Lay the radiant heating underlayment into the thinset. Check the underlayment instructions for installation details, as some underlayments may not require a bed of thinset.
Snap Chalk Line
Hammer two nails temporarily into the surface of the underlayment as anchors for the chalk snap line. Use the chalk snap line to create visual reference marks for installing the cable straps straight and evenly.
Glue Down Cable Straps
Heat up the glue gun by plugging it in. Run beads of hot glue along the chalk lines created earlier.
Lay Cable Straps
Quickly lay the cable straps in the hot glue before the glue hardens. Lay down only one strap at a time.
Run Cables Between Cable Straps
Build the first cable grid by looping the floor heating cables between two cable straps. Run the cable back and forth, following the marks on the cable straps, in a uniformly-spaced serpentine pattern. Keep the cables tight between the straps but not so tight as to pull the straps loose.
Floor heating cables should never be cut. For this reason, be careful when you calculate the length of floor heating cable prior to purchase.
Build Adjacent Cable Grids
Expand the radiant floor heating by building additional cable grids. These grids can be as large or small as necessary to fill the spaces, as long as the system's power output is sufficient.
Consider purchasing a radiant floor heating installation monitor. This low-cost electronic device is helpful as it can detect if any of the cables are nicked, cut, or otherwise damaged during installation. For less than $25 or $30, this device can save you thousands of dollars by keeping you from having to remove the tile floor to repair the cable.
Tape Down Cables
Use the high-temperature tape to secure the cables to the underlayment. Do this about every 20 inches. This helps to keep the cables in position and parallel until the tile is installed.
Connect Cables to Electrical System
Have an electrician install the thermostat to a non-GFCI electric circuit. The electrician should splice the floor heating cable into the electrical cable that leads from the circuit—mindful of the fact that the splice will eventually be embedded in wet thinset mortar. The system should also be tested with an ohmmeter or multimeter.
Trowel Thinset Over Cables
Trowel thinset mortar over the heating cables. Run the trowel in the direction of the cables. Be careful to avoid cutting, nicking, or disturbing the wires.
While the thinset is still wet, install the tile in the thinset. After the thinset is fully cured, grout the seams.