Q&A / 

How to Install Radiant Electric Floor Heating

Quick Column Summary:

  • How good is radiant heating
  • Calculate heat loss to determine heat needed for your room
  • Use separate electric circuit for mat
  • Do all of the testing steps

DEAR TIM: I'm remodeling a small room that has no heat. Radiant heating is really appealing to me because it's so comfortable. I've seen mats that go under ceramic tile or laminate flooring. Are these electric radiant heating mats reliable? Are they hard to install? Can you control them with a programmable thermostat to save money when you're not in the room? What other tips do you have to offer? Rachel M., Sandy, UT

DEAR RACHEL: I had the pleasure in the past few days of powering up an electric radiant heating floor system in a man cave I created for myself. It produced heat immediately and is going to keep me as snug as a bug in a rug while I operate my ham radio in the cave.

As with any product, you need to do your due diligence to ensure you'll have success. I spent some time online looking at the different products. Once I narrowed my choice down to two products, I then made sure the mat could keep the room warm.

Realize not all mats create the same amount of heat per square foot of mat. What's more, you need to do a heat loss calculation to determine the amount of BTUs you'll need to heat your room. Each of the websites I visited had a handy calculator to help you with this task.

This strange mat contains electric heating cables that can keep a room toasty warm. Photo Credit: Tim Carter

This strange mat contains electric heating cables that can keep a room toasty warm. Photo Credit: Tim Carter

You'll discover very quickly it's important the entire room is insulated for the radiant floor mat to work well. I was very fortunate to be able to insulate the floor under the mat as well as the walls and ceiling. Doing these things kept my heat loss to a minimum. It doesn't take much electricity to keep my small room warm.

The radiant floor mats are very reliable. They can last for years if you take very simple steps to ensure the mat is not damaged during installation. The mat I selected came with a dandy little electronic monitor that told me during the entire installation process my mat was in perfect working order.

I would say the degree of installation difficulty is moderate. You'll need an electronic multi-meter to tell you if all is well with the mat even if you do purchase the monitor. It's very important to check the resistance of the heating cables before you start, as you install the mat and after you cover the mat with the required layer of thinset or self-leveling compound. Multi-meters are not too expensive and you'll be able to use it to troubleshoot other electric problems around your home.

You'll need to extend a separate electric circuit to the room to power the mat. The size of this circuit depends on the number of watts of power the mat consumes. Be sure you extend the correct cable that can handle the load. This electric cable is installed in a standard electric box that's nailed to a wall stud. The mat's thermostat will be connected to the power cable in this box. Be sure you strategically locate this electric box so the wires from the mat can reach it. You do not want to splice wire onto the mat cables.

My instructions said to embed my mat in a bed of thinset. Thinset is the same mortar you use to install ceramic tile. It's easy to mix and apply. My instructions said to make sure the notched trowel lines of the thinset were parallel with the cables in the heating mat. After you apply the thinset to the clean subfloor, you roll out the mat onto the thinset and smooth the mat out making sure there are no bubbles or high spots. It's not hard to do.

The next step for me was to cover the mat with a one-quarter-inch-thick layer of thinset. This is the hardest part of the job in my opinion. This final surface that protects the radiant heat mat must be flat so your finished floor is easy to install.

Because my mat sat up 1/8 inch above my wood subfloor, I decided to install strips of 3/8-inch thick by 2-inch wide pieces of plywood on the two long walls of my small room. I cut a straightedge from a straight piece of 1x2 finished lumber that sat on top of these wood strips. I wiggled this wood straightedge back and forth across the wet thinset so the top of the thinset was in the same plane as the top of the plywood strips. It worked perfectly.

My radiant mat came with a wonderful programmable thermostat. I'm able to program in four different time periods for each day of the week. It also has a manual override in case I need the heat on at a time it's normally set low. This thermostat will save money because I'll only heat my room when I'm using it. My thermostat had a special setting for laminate flooring.

Be sure you read all the instructions that come with the mat and thermostat before you start the job. The location of the thermostat is very critical. My thermostat came with a sensor that must be installed just under the finished flooring. You need to be sure you can easily run the small wire to the thermostat and it not get damaged.

Don't skip any of the testing steps. Record the resistance readings and make sure they're within the range called for in the written instructions. If you have any questions, STOP and call the manufacturer. Once your mat is covered with thinset, you'll not be removing it without ruining it. You must make sure you're doing everything correctly as the job progresses.

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