Tile 101: How To Install SunTouch WarmWire Radiant Floor Heat

The cat and I both agree, there’s not a whole that can compare with walking barefoot into your bathroom and feeling a toasty warm floor under your toes. Or, in the cat’s case, under your body that is conveniently stretched out in the middle of the floor to trip unsuspecting humans who try to encroach on your domain.

We shouldn’t encourage this behavior but it was too hard to pass up having a warm tile floor in the master bath, even if we have to risk stepped-on tails and sprained ankles every time we walk in there.

Installing the radiant floor heat was actually a pretty simple project. Here’s how it went down…

Toasty Toes: The Basics

There are types of floor heaters that are meant to actually heat a space (in place of forced air or space heaters) and there are types that are just meant to keep you from making a squinch-face when your bare foot hits a cold tile in the middle of the annual midwestern ice age winter.

Hydronic radiant floor heat that circulates hot water through pipes (usually set in a concrete slab) is most often the former– in the manufacturing plant I used to run we had hydronic radiant floor heat in our kiln which kept a 5000 square feet area well above 100 degrees 24 hours a day.

Electric wires set in mats or by hand are generally better for light heat applications. These can be set on concrete or plywood, and can be specifically designed for use under tile, wood, or carpet.

We originally looked a electric floor heat that was pre-wired into mats, like these from SunTouch.

Installation of these mats basically consists of rolling them out and fastening them to the floor with tape or hot glue before covering with thinset and tile. (More on installing floor tile here.)

I used this system in the bathroom of my old house and it was fairly cheap for a 5×7 room. For a 8×12 room, things started to get a little more pricey. The SunTouch WarmWire (basically the heating wire without the mat) was a much more cost effective option.


It also requires a little more work on the installation side, but you know I don’t have a problem trading a little manual labor for a few hundred dollars in savings.

Installing Warm Wire

What I Used:

I purchased a 60 sq ft kit that included:

  • 60 sq ft of heating wire
  • 2 rolls of double sided tape
  • 2 coils of metal strap
  • Programmable thermostat/control
  • Installation monitor

Other tools and materials needed:

  • Metal snips
  • Galvanized deck screws
  • My heart drill
  • Wood chisel and hammer
  • Electric tools and/or a Chief Electrician
  • Thinset mortar
  • 5 gallon bucket
  • Drill mixer
  • Flat trowel

What I Did:

Step 1: Read The Instructions. Seriously.

There are times when I’m an advocate for figuring things out as you go, but when dealing with a not-cheap heating system (something that involves heat and electricity– both things that could burn down your house) I recommend doing your homework.

I read the online manual (here) about three times before even purchasing the system and then again before I started the installation. I also watched the DVD that came with the kit.

Prior to purchasing anything we had to figure out the basic layout and how many square feet we were going to use, but I also marked everything out with tape before getting started to be 100% clear on what I was doing ahead of time.

Here are a couple of key things I learned from memorizing the manual:

  1. You can choose the spacing of your wire– 2″, 2.5″, or 3″– but never ever space the wire closer than 2″ unless you want to burn your feet and set your house on fire.
  2. Plan to insulate under a wood subfloor for maximum efficiency.
  3. The WarmWire cannot be cut, if you buy 60 square feet, you need to use all of them.
  4. WarmWire can be installed over plywood subfloor but an underlayment is still recommended for tile.

Step 2: Setup

Other than the layout, you also need to plan for how/when to install the electric components. Its recommended that the floor heater be on a dedicated breaker and you also have to be able to get power to control box, and then power and temperature wires from the box to the floor. Since we ran the wires for  the electric straight into the basement, we wall fished the wires from the mat up through the wall to the box. And by “we” I mean our Chief Electrician. God bless him.

Another thing that needed to be done was to set up the installation monitor. This little gadget hooks onto the the wires (that should not be hooked up to power) as you’re installing, and if you accidentally cut one it lets you know. You’re still screwed, but at least it’s not a surprise after the entire floor is installed.

Here’s the monitor (called a Loud Mouth):


It runs on a 9v battery:


And you just connect the three wires from the heating wire and turn the monitor on:


It’s well worth the peace of mind while installing:


The other thing that needs to be planned for is where the factory splice and thermostat wire will be placed. These areas of floor will need to be chiseled out a bit to keep from creating high spots in the floor.


Step 3: Metal Strap

The metal strap is what holds the heating wire in place. It was easy to cut to size with metal snips.


Then using double-sided tape I attached it to the floor.


I started out sticking the tape to the floor and then putting the strap on top of it, and about half-way through my mom asked why I didn’t just put the tape directly on to the strap. Which was 1000 time easier.


Point to Mom.

And speaking of Mom, she spent Mother’s Day getting acquainted with my drill and helping anchor down the straps with galvanized deck screws.


Here we are, ready for wire.


Step 4: Running Wiring

I chose to do 2.5″ spacing for the wire. Stringing it out was pretty easy.


My mom fed the wire to me as I worked, and it was a pretty quick job.

12 _direction_change

You can see we basically kept the heater to the main walking area instead of doing the whole floor.


I kept it pretty close to the cabinets and tub since we assume those will be high traffic areas.


The wire should be kept at least 6″ away from the wax ring of a toilet. I left about 9″.


You can see we (and by “we” I mean “the Engineer”) planned pretty well with only 12″ of extra wire.

Once the wire is strung the Loud Mouth can be disconnected and and the heating wire and thermostat should be connected to the control unit and main power.   Our Chief Electrician hooked everything up and we did a test run to make sure everything worked properly. Since everything was nice and toasty, we turned it off and I mentally prepped myself for putting down a layer of thinset.

Step 5: Thinset Layer

There are a couple of ways you can do this. One way is to cover the wires with thinset then put down a second layer of thinset with a notched trowel while it’s still wet and install the tile right away. Another is to pour self-leveling concrete over the entire floor, let it set, and then install your tile. Or you can trowel on a smooth layer of thinset, let it set, and then install the tile.

Originally I wanted to do it all at once. I don’t have a lot of faith in self-leveling concrete or my untested abilities to trowel on a smooth, level layer of thinset. However, I also want to install the 18″ floor tiles in this room on a diagonal, and attempting to do that while covering the wires seemed like taking on a little much all at once. (Says the girl living in a garage and building a house in her spare time, right?)

So I decided to attempt troweling on the thinset in a smooth layer and letting it cure.

I mixed a batch of polymer-modified thinset in a five-gallon bucket using my trusty drill mixer.


Looks magical, but is probably grounds for wearing a dust mask while mixing.


Then I started with a couple blobs of thinset:


And smoothed everything out with a straight trowel to about 1/8″:


Just enough to cover the wires and keep everything level:

20_thinset done1

The first few square feet took the longest, but once I got the hang of it, it wasn’t so bad. Since I was using a metal trowel I took extra care with the wires… nicking one at this stage would be disastrous.


It took a couple of hours to get the entire room done:


I feel pretty confident in the result. Even if I didn’t get everything precisely level, I can’t be more than 1/8″ off, and I can always make up for that when installing the tile.

The thinset will take about 24 hours to cure, and the next step is a standard floor-tile installation. We’ll have to wait a few weeks as the tile and grout cures before turning the heater. In the meantime you can check out this post for more on installing floor tile, or this post for more tiling basics.

And in the course of writing this post, I realized that I totally forgot to clean the mixer attachment, so I’m going to go spend some quality time with a hose and putty knife scraping it clean now. Don’t tell MysteryMan.

16 Responses

  1. We did a tile warming system in our last house and the cat refused to get off the bathroom floor. If we picked her up to move her out of the way she would cling the the bath mat in a frantic attempt to stay on that wonderful floor.
    Did you have any trouble with the heating wires lifting or twisting on long runs? Ours kept trying to lift so the manufacturer suggested using heating duct tape to keep them down.

    1. The way I laid out the system the wires were only running 3ish feet between the straps so I didn’t have any big problems. To keep the thermostat and splice in place while grouting we used a touch of hot glue (at the manufacturers suggestion.) I think heating duct tape would be a good solution too though… less likely to cause burns for sure.

  2. Saved for later! We want to put heated floors in both of the bathrooms we’re remodeling this year (or at least starting) as they can get chilly especially with the low temp heating from the forced air geo system blowing right on you (the only good place for registers is right next to the shower). We wanted to not use the mats to save money too. I’m excited to see how it turns out. I’m worried about uneven troweling because we want to used large format 18×18 tiles in the master bathroom and the tile supplier & manufacturer both say you need a perfectly level floor for them.

    1. My tiles are 18×18 so I’ll let you know how it goes. You could also place them when you cover the wires or use a self leveling concrete if you’re worried about troweling it on!

  3. Great job! Due to a frozen shower/bath valve and consequent leak, we have decided to replace the bath with a shower, radiant heat, tile and, of course, better insulation :). You have educated me far better than the manufacturers’ web sites. Any thoughts on 110 v. 220 volt heating systems? Have you documented the rest of your house construction as well as you have explained this project?

  4. You GO Girl ! Right On! It’s Very Assuring when a young lady steps up .So as us OLD GUYS DON’T FEEL SO BAD , When we are surfing the web confused & looking for answers .Thank you very much young lady .Now It’s Back 2 Work ! Thanks Again ! Philip in California . OUT&Bye

  5. Nice tips. We get a few clients that can’t afford our heat pumps and radiant floor heat is a good option for them. We’ll send them this way if they want to go that route.

  6. I was thinking on installing some in floor heating system in my house because I’m redoing the floor, but I am not sure of the electrical part I will hire an electrician but don’t know we’re should I start it or finish it for this to be done right, does any outlet works?

    1. No, it needs to be hardwired, so the electrician will need to put in a new box. I’d have them do that before you start.

  7. Just wondering how well it has been working since you installed- does it keep the heat well? Cost to run what you thought it would be? I am considering heating a whole floor- about 440 sq Ft and because of size and shape need to keep the wires towards the middle of the room. Does the heat extend out? Or only heat what is above it? I appreciate the help!

    1. While I no longer live in this house, the floor heater worked great. It doesn’t keep heat much beyond when it’s turned off (5-10 minutes maybe) but there’s not a noticeable cost to run it. It really only heats what is directly above it, there’s no radiating outward, so you can definitely tell which tiles have the heater under them and which dont!

  8. When installing radiant heating do you mudd only and then lay tile over the mudd? My contractor wants to lay mudd and install wonder board over the mudd and then use thin set to install tile. I am afraid if the wonder board shifts will it crack the tile. Can you offer any help.

  9. Thanks for sharing your photos and experience. For accuracy sake, you should make a distinction between “square feet” and “linear feet”, when discussing the product, especially in regards to the “warm wire”.

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