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Full bathroom remodel, part 5: laying a heated tile floor

Jim Mallery | Improvement Center Columnist | March 2, 2015

Fifth in an eight-part series on bathroom remodeling

In part 4 of this series on DIY bathroom renovation, we discussed building a custom tile shower from the ground up. Now we'll show you how to install a heated tile floor to keep your tootsies warm as you step out of that shower.

Nowadays, if you're reflooring the bathroom, you should consider heating the floor, even if you don't own a luxury home.

An average heated bathroom floor can cost as little as $250 to $300. The Home Depot and Lowe's carry heating systems aimed at DIY bathroom remodeling, but because this is a project that involves some electrical wiring, you might want to contact a bathroom remodeling contractor. The systems are not complicated, however. A mesh mat with a heating wire is embedded in mortar. A thermostat attached to a heat sensor in the floor controls the temperature.

Finding power

floor wiring

The hole in the wall for the thermostat with the power supply line; the power line to the mat; and the thermostat sensor waiting to be trimmed back and attached. To get power, a receptacle box in the next stud bay was tapped.

The power source is your greatest concern. Manufacturers recommend a dedicated circuit, which might mean hiring an electrician. Even if you are confident in your wiring abilities, it can be pretty difficult to run new circuits in some houses -- and that is assuming that you have room for another circuit in your service panel.

But often, you can tap into an existing circuit. The heating pads don't draw much power: A 30-square-foot pad -- which would heat a spacious master-bath floor -- draws only 3 amps. If you were heating a large room, you would truly need a dedicated circuit, but the small square footage of most bathrooms makes using an existing circuit an option.

thermostat for heated tile floor

The digital thermostat lets you program when the floor is heated.

 

Some digital thermostats designed for use with a heated bathroom floor have a ground-fault interrupter built into them. If that is the case, you cannot tap into the bathroom power, which is already on a GFCI circuit, because two GFCIs on the same circuit won't work. If you have a choice between a 15- or 20-amp circuit, go with the 20-amp.

Also, remember that you only need to heat the areas of the floor on which you will walk -- not under the shower and not behind or beside the toilet. Keep in mind, too, that the heat does not travel far horizontally: If you are stepping a few inches away from the pad, the tile will be cold.

The installation

Assuming you are installing a tile floor -- porcelain or stone -- here are the steps for laying the heating mats.

installing floor backerboard

The 1/4-inch backerboard with joints taped and filled with thinset is ready for the floor-heating mat.

 

floor pad and tile

A thick layer of thinset mortar, and then marble tile, goes atop the heating mat. When doing the tile in a one-step process, with a thick coat of thinset over the pad, you must be extra careful to level the tiles. Alternatively, you can cover the mat with a coat of thinset, let it harden, then lay the tile with a traditional layer of mortar. Note the wire to the right, which is the heating sensor cable that runs to the thermostat. The sensor is embedded in the middle of the pad.

 

  1. Backerboard first. As with any tile installation, lay backerboard over the plywood subfloor. Quarter-inch backerboard is all you need. There are numerous options for backerboard; just remember to follow the manufacturer's instructions. Usually it's nailed or screwed over a layer of thinset mortar. The joints are then taped and covered with thinset.
  2. Matted down. Carefully follow the manufacturer's instructions. Usually, the mat can be attached to the backerboard in several different ways -- with staples, double-backed tape or hot-glue gun. Two important notes: Be careful not to staple the actual heating wire or in any way damage it, and pull as much slack and wrinkle out of the mat as possible as you secure it to the floor.
  3. Top coat. The mat is covered with thinset and tile. You have two options: You can coat the mat with mortar, let it set, then lay down the tile with another coat of thinset; or you can put down the tile all in one step -- a thick coat of thinset over the mat and the tile atop it. The latter option is quicker, but can be a little tricky to keep level as you are trying to set the tiles over a deeper soup of thinset.
  4. Wired. Run the power lead and temperature-sensor wires through the wall's base plate and up the wall to the thermostat, where they should meet up with the house current that you have already provided.

heated tile floor completed

The heated marble floor awaits you to warm your toes on a cold winter morning.

 

Heated floors mean a little more work and expense, but your toasty toes will thank you.

Next, part 6: installing the vanity

About the Author

Jim Mallery, a semi-retired journalist and onetime registered contractor, has extensive experience remodeling, repairing and rebuilding homes.