One of the best upgrades for a bathroom or kitchen tile floor is the use of in-floor heating. There are several different products available to accomplish the coveted ‘warm tootsies when it is forty below’. One of the more popular products (around here, anyway) is the Suntouch WarmWire radiant in-floor heating. That’s just a really long term for wires that heat your floor (and warm your tootsies).

Now that I’ve used the word ‘tootsies’ twice in one paragraph I believe it’s time to move on.

As an ‘official’ reference the manufacturer’s installation guide can be found online in one of those fancy-ass pdf thingies HERE.  It contains all sorts of things that you need to be aware of before starting your installation. While this post will walk you through how I do it, your installation may differ in aspects of which you are unaware. You need to read through the manufacturers information as well before you actually install you WarmWire.

This is as close as I’ll ever get to an official disclaimer: Be aware that the methods I use will differ somewhat from the manufacturer’s instructions intended for the do-it-yourselfer. I am a professional tile guy (really – what are you laughing about?) I accept liability with everything I touch in a customer’s home and accept that risk with the methods I choose to utilize. Read the manufacturer’s instructions before installing your WarmWire!

This information focuses on the installation of the substrate below the WarmWire, the installation of the wire, and the installation of the Schluter Ditra membrane above the wire for the purpose of tile installation. The technical aspects of the electrical wiring are covered only briefly and in very basic terms. They are not meant to be a definitive guide to properly wiring the WarmWire underfloor heating element to your control box and power supply. READ THE MANUFACTURER’S INSTRUCTIONS REGARDING YOUR PARTICULAR CONTROL BOX! In English that means if your house blows up it isn’t my fault – I was all the way over here.

In your area it may be required to have an electrician wire your heating element. Check with your local building codes to make sure. If it’s required and you don’t do it you could be in heaps-o-trouble. Don’t mess with the city codes, they’re not very nice if you piss them off. Trust me on that.

Ass covering over – lets get on with it.

The WarmWire system consists of two basic elements – the wire and the control box. The control box is hard-wired to your house’s electrical system and the wire is attached to the control box. The wire is then routed down behind the wall and under your floor. After installed you can essentially control the temperature of your floor tile with the control box.

Before you begin you need to figure out how much WarmWire you need to purchase. The above referenced pdf contains a chart which will explain which wire you need based on the square footage of the floor in which it is being installed. There are three different spacings which can be used and utilize different wattage per square foot. That’s all just confusing crap so I’ll explain it like this: The closer you place your wire the warmer your floor will be – and the more power it will use to accomplish that. Easy enough, yes?

How long your wire needs to be depends on how much square footage you’re heating. The quick way I figure it out is the square footage of the room multiplied by 0.90 (because there is no need to heat along the walls, in closets, etc.) and multiply that by 4.7. That will give you the approximate length of the wire you need.

The wire is available in pre-measured lengths. It is not something you can just order to a specific length. It is a closed loop wire which means it is one complete unit and not a wire that can be cut to length. So you need to figure out the length and order the closest to that number.

The different spacings are 2, 2 1/2, and 3 inches. For the purpose of this post I will use the 2 1/2 inch setting as that will be the most commonly used – and because that’s what I have photos of.  You need to also purchase the wire straps which will attach the wire to the floor and hold it in place while you install your flooring above it. Do not use nails, screw, etc. – use the straps. They have pre-spaced clips to hold the wire in place correctly. And using any other method you risk damaging or severing the wire.

For this particular installation I chose to use 1/2″ Hardiebacker cement board on the floor with the heat wire installed to it. Above that I used Schluter Ditra membrane for the tile substrate. When using Ditra you want your heating element, whether it be the wire, a mat, or other type, beneath the Ditra – not between the Ditra and tile.

You can click on any of the badly taken photos for a full-size version.

Installed Backerboard Substrate

Figure 1

Make sure your Hardiebacker, or whichever substrate you use beneath the wire, is installed correctly for a proper tile installation. This is imperative since it is the very base layer for your floor. If not done correctly you risk compromising the entire installation – pay attention, this gets expensive! Read How to Properly Install Backerboard for Floor Tile.  Check out that link – I’ll just sit back here and have a beer Pepsi while you do.

Allrighty! (I can’t believe I just typed that) The first thing to do (after properly installing your substrate – in this case hardiebacker – figure 1) is to install your straps. The metal straps made for WarmWire have tabs every inch. I’m certain you can figure out how to use them for whichever spacing you’ve chosen.

Installing WarmWire Straps

Figure 2

Installing WarmWire Straps

Figure 3

For this particular installation I’ve used every third tab in some areas and every other tab in others. I do this to make the floor warmer in certain areas (in front of the shower and tub) and less so in other areas. I do not know if this is standard practice or not – it is for me. If you are concerned about it please see the ‘disclaimer’ at the top.

The straps are placed on the floor and screwed down. (figures 2, 3)  Suntouch recommends using a spray adhesive to hold the straps in place until you get them screwed down – I do not do this.  I have no problem keeping them where they need to be without it and I do not like any foreign substances beneath my tile installations, especially one to which thinset may or may not adhere.

Close-up of WarmWire Heating Elements and Straps

Tab Spacing

I place the straps every four feet to hold the wires in place. I find this gives me enough hold for what I need to do above the wire before the mortar is fully set. Once that happens they won’t go anywhere anyway. But you do need them to be held in place until that point. Don’t try to use a shortcut with this part, if you damage the wire you’ll need to 1. pay to replace it and 2. start over. Neither of which are my preferred method.

You may want to invest in the electronic box Suntouch makes called the ‘LoudMouth’. It is a small electronic box with a 9 volt battery which you hook the wire to when you start your installation. If you damage or sever the wire at any point the box will scream obscenities at you, call you names, light your dog on fire, or something that will let you know in no uncertain terms that you have screwed the pooch (hopefully not while it was on fire).

If you do damage the wire you can purchase the splice kit with which you can repair the damaged wire. I’ll cover that in another post – hopefully one nobody will need to read.

The end of the WarmWire which is attached to the control box is twice as thick as the heating part of the wire. You need to start your wire placement at the base of the wall beneath the control box. Unroll the WarmWire until you get to the smaller part of the wire – the heating element – and place that part of the wire at the base of your wall. In basic terms you do not want any of the thicker portion of the wire beneath your floor – only the thinner part.

Now the fun part. Starting at the point at the base of your wall start stringing the WarmWire back and forth across your floor utilizing the proper tab spacing for your wire distance. In the close-up photos I have it installed in every third tab. Place the wire beneath the correct tab and push it down to hold it in place. DO NOT use a hammer, screwdriver, or beer bottle Pepsi can to pound or push the tab down.

Installing WarmWire Heating Elements

Figure 4

Installing WarmWire Heating Elements

Figure 5

You want to start at one side of your room and end at the other. You NEVER want to cross the wires over one another. They need to remain a minimum distance of two inches apart at all points. Plan accordingly. This is why you want to get your layout figured before you start.

This is tedious but take your time and get it correct. It is imperative for proper performance of your WarmWire.

Installed WarmWire Heating Elements

Figure 6

The end of the WarmWire is a bit thicker than the wire itself. I will usually take my knife or a screwdriver and cut a small groove into my backerboard or subflooring in which to place the end. Ideally you want the end of the wire to end up at a wall in which case you can simply tuck it between your backerboard and the wall footing (you left a gap there, right?) but sometimes you need to end it in front of your vanity or tub.

I do the same thing with the probe. There is also a temperature probe which must be placed beneath your tile to regulate the temperature. It is thicker than the wire itself also. You can simply cut a groove out of your subflooring in which to place it.

Installed WarmWire Heating Elements

Figure 7

Once you are finished stringing the WarmWire over your floor you need to take care to not abuse it. You can walk on it but don’t dance on it, know what I mean? Take a break – you deserve it. When I sober up post the remainder we will cover how to install Schluter’s Ditra tile membrane over your Suntouch WarmWire for your tile installation.

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Leave a Comment

  • John Lammers

    Can you use warm wire with schluter dirta heat mats instead of the straps?
    Can self leveler act as base for tile?
    Kitchen with 3/4 plywood sub floor over 3/4 pine

    • Roger

      Hi John,
      1. Yes, you can use a warmwire system with ditra heat mats.
      2. What do you mean by ‘base’? It can be used as your substrate, but should not be used IN the heat mat. If you want to use both heat mat and slc the slc should be put down first, then the heat mat installed over that.

      • John

        Thanks that helps a lot

  • Roger

    Hi Charles,

    1. If you’re using plywood over it the acceptable variation is normally no more than 1/4″. Technically 1/4″ in ten feet with no more than 1/8″ in any two feet.
    2. I would use 1/2″ ply, it will be fine with ditra heat. 1/4″ notched trowel compresses to 1/8″. Your total overall height with 1/2″ plywood and ditra heat will normally be about 1 1/4″.
    3. All-set is fine. However, you do need a modified thinset between plywood and the ditra.
    4. I wold honestly replace any planks that need replaced. Why are you saving it? Either save the planks or install tile – you can’t really do both and have a solid tile installation.
    5. The house next door was more than likely done over a mud bed. And yes, they are essentially bulletproof.
    6. Lippage systems work well if used correctly. If the demo ‘pulled’ a tile up to bring it flush with the tile next to it – they were being used incorrectly. Correctly used the system pushes the high tile down into the mortar to bring the tiles flush.

  • Robert Smith

    Find myself in position in which I need to build a shower base from scratch and have not done this before. Found your information most informative. One of the most interesting and clearly written instructions I have seen on the internet. Do you make money with this? How?

    Thanks for the help on my project.

    • Roger

      Hi Robert,

      Yes, I make money on my knowledge. I really am a professional tile contractor. :D If you are speaking about this particular website – I have manuals available for installation instructions in the Library. Those normally make enough to pay for the website costs and a six-pack or two.

  • Mike

    I have a cabin in northern wisconsin. it has a concrete floor. our only heat is wood stove and single forced air heater. We are looking at options to overcome the frozen floor in the deep of winter when we visit (not keep on all the time). Is this something that would allow us to stocking foot walk or sit on the floor if this was installed on the concrete with some flooring over it? I understand some warming time would be needed. The cabin floor space is mostly open concept with a 750 sq ft concrete floor. Any other options would be appreciated.


    • Roger

      Hi Mike,

      It would be an ideal solution for your situation. It will also heat up the ambient room temperature. A lot of people use them as the main heat source in a room.

  • Kevin Overholt

    Hey Roger. I am installing Prodeso Uncoupling membrane with the suntouch warmwire cable. My question is how long do I have to wait after putting the Prodeso down before I can get on it to put my cable in and lay tile.
    Great website and information! Thanks for your help!!

    • Roger

      Hi Kevin,

      You can do it immediately.

  • Genevieve

    Hi, We are remodeling our bathroom and plan to place the sun touch warmwire in the floor. We have the cement board down. Our floor is not flat currently. So we were thinking we would put the wire down and then use the SLC. Should we then paint a coat of the waterproofing stuff on the SLC and then tile on top of that? Is there a good way to transition from tile to carpet at the door if the tile ends up being higher than the carpet? Thanks!

    • Roger

      Hi Genevieve,

      You can tile right over the slc, no need for the barrier at all. Schluter makes all sorts of trims for non-flush doorway transitions. Check out their site, I’m sure you can find one that will work.

  • dan

    I’m planning on installing Tec skill set heating pads. Every example for cutting for length has them cutting the entire panel all the way accross. I’d like to cut about a foot off just half of the panel. I’ve not seen anything saying this would work or not work. Any experience with that?

    • Roger

      Hi Dan,

      No experience at all. I would call Tec, they can tell you.

  • Wendy

    I am wondering if you can answer a question that googling is useless with. I am installing a ditra heat system in my bathroom floor, and the manual warns against using area rugs over heated floors. I always have a rubber backed bath mat in front of my shower, and am wondering if i should skip running heating cable in this area. Pls help before i go mad.

    • Roger

      Hi Wendy,

      The issue is heat build-up. Unless your thermostat sensor is under the rug, the area under the rug will build up excessive heat (because it gets trapped beneath it with no way to dissipate) and may cause issues with the entire system. If it is not a large rug I’ve never seen issues with it – normal bathmats are usually just fine. But I would lose the one with the rubber backing, forego the cable beneath where the rug goes, or place your sensor in the same area beneath the rug. The last one will lead to the rest of the floor not being as warm.

  • Carl

    Hey Roger,
    WOW, what a great site! you gave me so many answers to so many questions that I’ve had for years……. however here are a few more.

    I am building a somewhat barrier-free 3’x5′ shower (with no threshold), I have my sub-flooring all set up to create the pitch for my mud base (3/4 ply between the joist inside the shower and double 3/4 ply on top of the joist through-out the rest of the bath).
    my plan was to use 1/2″ hardi backer on the shower walls, redgard it, and then use 1/4″ hardi backer on the floor in the main area of the bath, next I planned on putting down my pitched mud bed with a schluter drain assembly, and then use Kerdi on top of the mud bed and integrated drain which I would lap up my redgarded walls 2″-3″s and carry out on top of my 1/4″ hardi board through out the rest of the bathroom (using Custom’s uncoupling mat mortar).
    Now for the curve-ball, I was told I am putting electric heated floors through-out. (by the way I am trying to conserve height as my 3/4″ ply is flush with the hardwood in the hallway now)
    1. is the uncoupling mat mortar a good seal between the kerdi and redgard?
    2. is the uncoupling mat mortar ok to use on the marble (3/4″ x3/4″ octagon) mat tile and glass accent tile on the floor?
    3. should I use the same mortar on the porcelain/ceramic wall tiles?
    4. should I just put the wire under the kerdi (following specs and you’r tips) and proceed as planned?
    5. Or should I change my plan and instead of using 1/4″ hardi in the main area, run my wire on the plywood and mud base and then put ditra on top of it in the main area and kerdi on it in the shower? (or ditra heat mat maybe?)
    6. if i use ditra how would I prep it for such small tile? (sorry I think i already read your answer to this one, but I was reading your page for hours last night and I don’t remember your answer)
    thanks in advance for your advice and CHEERS!

    • Roger

      Hi Carl,

      1. Yes.
      2. It is with the marble, the glass requires modified thinset.
      3. Yes
      4. Yes
      5. Ditra heat is you BEST option. Really. Otherwise, just run the wire on the ply and mud, then ditra and kerdi over it.
      6. Tile smaller than 2×2 should not be used over ditra. It may be fine, it may not. If that is the tile you are set on then I would just run your wire then use slc in the bath and kerdi in the shower.

  • dave

    I want to clarify a comment you make above. I want to use Ditra heat mats to install my heated floor. Can I use a different brand of wire and/or thermostat? Do you recommend a brand? Also, should I use the following install guideline:

    red guard(don’t know if this is necessary but it’s an upstairs bath)
    dirta mat

    thanks, Dave

    • Roger

      Hi Dave,

      I regularly use suntouch heating wire in ditra mats.

      You don’t need the hardi, don’t need the redgard (if you want it waterproof use kerdi over the seams after you put the wire in). The rest is correct.

  • Tim

    Hi Roger,
    Getting ready to do install with Ditra heat but would like to use warmwire or warming systems cable instead of Ditra brand. I am getting a lot of conflicting info about spacing of cable. Should it be every 3 spaces/ posts (3.5 inches), every 2? or 2/3/2? What is your preference / experience?

    • Roger

      Hi Tim,

      Every three, if you haven’t done it yet. Sorry, you got lost in the shuffle somewhere.

  • Alia

    Thanks for all of the great info. Have read most of the responses and still have a couple of questions We have 1″ osb and were planning to attach the sun touch warm wire cables directly to the osb and then cover with thin set or slc (debating cost vs convenience) but you mentioned primer in one response…latex sealant? Adhesive? What do you recommend? Also, we weren’t planning to use the ditra mat in between slc and tile…. What is the benefit? We will be adding sun touch to family, dining, kitchen during this Reno is that extra step (mat) worth it for these areas? Thanks a bunch!!!

    • Roger

      Hi Alia,

      Each brand of slc has a specific primer – that’s the one you want to use. And you want to install it over the osb before you install your wiring, to ensure full coverage. If you use slc ditra is not required, but it will definitely give you the added advantages of lateral movement dissipation as well as help even out the floor heating.

  • obie

    Can you install Suntouch Warm Wire in a wall?
    Is material UL Listed for wall installation?
    Architect want to create “warm wall” in bathroom.

    • Roger

      Hi Obie,

      That is a question for suntouch tech department. I’ve done it – by framing out a box with backer, installing the wire, covering it with mud, then tiling over it. As far as it being UL listed – I honestly have no idea.

  • Donald

    Have you had a chance to use the ditra-heat system? Any comments? Your experience with tile, in relation to this fairly new under floor heat system, would be valued greatly!

    • Roger

      Hi Donald,

      I have used it a lot. I will NEVER install in-floor heat with any other method again. It is that easy. (Suntouch and nuheat wires fit into the mat, much cheaper. Just sayin’…) :)

      • Russ

        Hi Roger,

        I will be installing 1″ x 2″ marble basket weave tiles (the dots are 3/8″) in my bathroom (over hardiebacker) and would like to install electric floor heat.

        I noticed in your response above that you prefer Ditra Heat, but the manufacturer specs say for tiles 2″ x 2″ or larger. I’ve seen information in other places on the web suggesting pre filling the Ditra Heat with thinset or SLC before tiling would work.

        Any experience with this small tile over Ditra?
        Have you used approach before ?
        Should I use a different heat system with a regular Ditra above the heating wires?

        Many thanks, your site has been extremely helpful !

        • Roger

          HI Russ,

          Regular ditra has the same size limitations. SLC would likely be your best option.

  • Katie

    Hi there. Is installing in floor heating a different installation process than tile? I have found that White Oak works best with wood? Any input is greatly appreciated! Thanks, Katie

    • Roger

      Hi Katie,

      I don’t quite understand your question. Do you mean is it different beneath wood than tile? If so, yes, it is different. You’d need to contact the heating manufacturer to find specifics. I don’t do that and wouldn’t know how to tell you what needs to be done. If that isn’t what you meant, you’ll need to tell me what you mean. :D

  • john


    Can i install Suntouch electric heat under tile shower floor ?

    Is installation different for Kerdi vs. traditional waterproof system ?


    • Roger

      Hi John,

      Yes, you can. And yes, it’s different. In traditional floors it must be in the center or towards the top of the top mud deck. In a kerdi it goes directly under the kerdi.

      • john

        hi roger,

        follow up question. My installer wants to use a kerdi show pan system. Can the Suntouch be installed on top of this pan and under the kerdi membrane ?


        • Roger

          Hi John,

          Yes it can (provided you have the suntouch wire approved for use in wet areas – I believe all suntouch products are now, but I’d call to make sure).

          • John


            One more question. Installer has talked with Schluter and they recommended using Ditra Heat in the shower since I will be using heat cable vs. a mat. I know it makes for a quick installation of the cable vs. cable strips and thinset and then Kerdi.

            So I will have Kerdi shower pan / drain, ditra heat with electric floor cable (approved wet). Walls will be drywall / kerdi membrane.

            Should I also put Kerdi on top of the Ditra heat since the cables will be buried in the Ditria heat ? Or is the Kerdi on top of ditra heat just overkill ?


            • Roger

              Hi John,

              In an application like that you would have the ditra heat directly to the mud bed, then the drain is installed over that, then the kerdi goes on top of all of it.

  • Doug

    I am about to have a contractor lay a floor on a concrete slab that is about 10 years old, has not cracks and is loaded with rebar and mesh wire – has no cracks and I doubt it ever will. The floor was leveled today with SLC and is fairly level. Then, we are going to use regard as there have been some water issues in the past, which have been fixed, but just to be safe, I wanted to use it. Then, we are going to use thinnest OR glue and use Cerazorb, then the heat mat with thinset and then thinset and tile. So:

    Thinset with heated wire
    Slate tiles

    I noticed that you like Ditra, but is it necessary.
    Also, could we use a waterproofing glue over or instead of the Regard.

    Will the Redgard offer any further insulation value under the Cerazorb?



    • Roger

      Hi Doug,

      Ditra is not necessary. Do not use waterproofing glue, the thinset will likely have a problem bonding to it, especially with heating wires embedded in it. Redgard will not give you any significant insulation value. It is a VERY little bit, but not really enough to change anything.