The house took me seven years to build so by the time I was ready to actually tile the room they had come out with some heated floor systems for warming tile floors and I splurged and went with a single ribbon system instead of the mat system since my floor was oddly shaped.
I got it on EBay and can't remember what I paid but I think it was around $600 for the entire kit including a thermostat that keeps the floor just a few degrees above the room air temp. You can get bigger systems to actually heat the floor but that seemed to expensive and unnecessary in Florida.
Step 1: Getting Started
I went as far as making the exact finished dimensions in a manner that minimized the amount of tiles I would need to cut. This might not be that big a deal if you're just doing one room but I did all my bathrooms, hallways, entranceways and the kitchen floor in tile so I had to put down about 1700 square feet of it. A little planning ahead goes a long way if you're just in the designing phase...
I used backer board for the walls of the masterbath and the heated part of the floor but in the rest of the house I did mudpans which if I remember I'll do another Instructable on and link HERE. (https://www.instructables.com/id/An-Alternative-to-Using-Backer-Board-over-Subfloor/ )
I chose not to heat the base of the shower itself because I didn't see anyway a low current system could keep up with water flowing over it's surface and I had to line the subfloor with a sheet of shower pan and didn't want to pierce it with the cable guides and I was also worried about running the heating coils up against the rubber. I didn't see much point in heating the floor under the vanity either so I chose the size of the heating strip accordingly, which was about 45 square feet.
Step 2: Sinking the Floor
I then framed in the seat and I plywooded all the walls of the bathroom since I did that to the entire house for hurricane protection. The shower pan / sheet of rubber, you basically just spread out on the floor and up about 6 inches on the walls and staple along the edges only. You don't want to pierce the floor itself with a staple and you need to tuck the corners in like your making a bed. The idea is to end up with basically a 6 inch deep bowl that would hold water. I put the drain at the rear of the shower close to the base of the bench since I didn't want a low spot for someone to walk over. This was just a personal choice you don't need much of a slope for the floor to drain across the tile and it worked out that I had plenty of room below that spot of floor to run my drain lines.
Since there was no wall between the main bathroom floor and where it began to slope to the drain I staple the mud pan to the floor again only at the edge and used backer board on the rest of the bathroom floor and over lapped it onto the rubber by about 2 feet. They make a glue I believe for making tight corners but I'm pretty handy and got a snug fit without it. I then used backer board on the shower walls and again overlapped it on top of the rubber but not much more than about 2 inches. Again this was a personal choice cause I know backer board is supposed to be water proof but I just didn't like the idea of having a cut edge resting right on the floor where it might wick up moisture so I dunno, use your best judgement.
I intentionally sloped the floor down much deeper than the final inch and a half drop I ended up with over five feet because I wanted to be sure the rubber was well below the level of the backer board on the main floor. The drain for this is actually a double drain and the first part seals the rubber to the subfloor and allows any water making it through the tiles and mortar to go down the drain instead of causing the subfloor to get wet.
Step 3: Installing the Heated Areas
They also make mats in various sizes if your fortunate enough to have a rectangle you want to heat which would probobly save some time on the installation.
This wire needs embedded in the mortor and although I believe it said you could use thinset but don't quote me, since I have a mortor mixer and sand is plentiful in Florida I used a sand and portland cement mixture with fiberglass that I got from the concrete plant up the road. It's supposed to be one bag of the fiberglass to a yard of concrete but I used about twice that much. I forget precisely how I arrived at that but with my mixer it was a bag of portland cement, half a bag of fiberglass and about 40 shovels of sand. I know this is an odd mix but it sets up very firm and so far in that past year I haven't had any failures in the 14 by 26 foot kitchen floor using the same formoula but over roofing felt over 3/4 tongue and groove plywood but it also stays soft enough for a day or two that you can sand it with a brick the next day without very much effort and get a smooth surface to lay your tile on.
I started at the far back of the shower and worked my way out of the room putting about an inch and a half over the shower pan at the bottom then smoothed it so it buried the wires by about 1/8 of an inch. I ripped some strips of treated wood 5/8 of an inch thick and ran a border of it around the walls I would be cementing to leaving about a 1/4 inch gap for expansion between the strip and the wall. I used this as a form to float the cement mixture and used treated wood so I could leave them in place. I had cut some extra strips and when I did a big room like the kitchen I would use them to temporarily float out the floor then I would go back and pick the strip out of the cement and finish it with a hand trowel as best I could.
This is where the sand it with the brick the next day comes in handy, you don't need to be a perfect finsher but don't get so far ahead of yourself you let it sit for longer than a day before you take a brick to it.
Step 4: Putting Down the Tile
I chose to use a tile that was in 2 by 2 inch squares to make it easier to do the curvy floors since I could vary the gap a tad and make subtle curves where bigger tiles would be a problem around the drain but I suppose it would still be doable.
I made sure that it dried almost a week to be safe before I wired in the thermostat and tested it. I ran a dedicated 20 amp circuit to a box in the wall about light switch high. The ends of the loop are insulated to go inside the wall up to the box and it's a simple matter of wiring it up as instructed. There is also a lead for the thermostat that gets mounted in the floor and basically the wall thermostat keeps the floor just a few degrees above whatever the room air temp is with an adjustment so you can make it very low power consuming and simply not feel cold when you walk on it with bare feet, or warm enough it's enough to have the dog want to sleep on it in the winter...
It also comes with timer so you can cycle it but since it is low heat you need to plan a few hours ahead.