No-- what he's doing is right. The coils go down first, then either thinset or self leveling compound goes over the top, and then the tile.

Warning on your layout, though. He's only got the wires taped at the turns, and there's significant variation in spacing as it now lays on the floor. That will result in variable warmth on the tile floor, and it'll drive you crazy. The wires need to be spaced evenly, something more like this:

Mongo and Weedy, thanks for your replies. I wondered about the layout, too, but thought to myself what do I know? Well Weedy, you are right. The way the coils were laid, the rest of the room (can't be seen in my picture, but it's the area to the left), the coils are spaced pretty evenly about 3" apart. The coils that are visible in the picture are in front of the shower area, and are spaced closer together with quite a bit of variation. I looked at the manufacturer's website (Warmtiles) and they have an installation video. This is not how they say to do it on the video. I called the company and spoke to a technician for verification. He said that it was definitely done wrong and needed to be fixed...it has to be uniform throughout the room. He even said that a few of the coils that I described as being about 1" apart were too close and would be in danger of overheating. So....the contractor pulled everything up yesterday and we are starting over. Now, he wants to put down mesh, then mud, then coils, then thinset over that. He says he will do the spacing however I want. My tiles are pretty thick, so the rep at Warmtiles said I could do an alternate spacing (instead of 3" throughout the room, I could have them do 1.5"/3"/1.5"/3" throughout the room. This layout is recommended on the Warmtiles website only for rooms that are over an unheated space, but this is not over an unheated space...the tiles are just a little thicker than normal. So, I am concerned whether that will be the best way and I'm confused as to what would really be the best layout. Would you do it 3" evenly spaced throughout the room or the alternate spacing layout like the rep suggested? I am concerned that the alternate layout will produce uneven heat. Help!

A membrane (practically Any membrane at all) will help physically separate the coils' heat from that concrete slab. I think I see a concrete slab in your photo. As much as possible, you do not want to heat up the entire slab, but rather just the tiles, thinset, and a bit of the slab. Unless of course you decide you DO want the slab to be warmer all the time. Your choice.

There are no membranes sold as thin heat insulators "per se" so you have to make do with a membrane, sold as a membrane, and let it help in insulating. I think one of the Noble company products is a membrane sold for crack isolation and it has a heat insulation rating too. That fact might make it better as an insulator, or maybe not.

Hot glue can hold the cables in place.

HTH.

Yup, I'd make him take a mulligan in that first cable installation. That's plain ugly.

Tile has a very low R-value, and thus transmits heat quite well. Standard spacing would likely suffice unless you get into the realm of thick saltillo-types of tiles...tiles over 1" thick.

I find their 1.5/3/1.5/3 recommendation a bit odd. With tile transferring heat so well, I'd rather the spacing be equal. In this case 2-1/4" all across the floor.

But hey...whadda I know?

Welll, you are right. It's almost like those cable manufacturers don't want us thinking for ourselves. Even spacing, and adjust it to suit. But I'll betcha lots of people will overdo it , though, if you let them adjust things any which way.

Here is a little bit more information that might or might not make a difference in your opinions: My tiles are approximately 1/4" thick. No concrete slab here. It's being installed on plywood. This bathroom is new construction on the second floor of my house, built over heated living space (my den). The bathroom itself has two outside walls, two inside walls, and hi-output baseboard heating will be the main heat source in the room. As I mentioned in my earlier post, the contractor pulled up the old installation yesterday. Today he came back and put down mesh and mud on top of that. The electrician will be back on Thursday when the mud is dry to put the cables back. Then it will get thinset, then tile. Mongo, why do you prefer 2 1/4" spacing throughout instead of 3" spacing? Would I get cold spots with 3" spacing across the whole floor? I had the contractor speak with the same Warmtiles rep that I spoke to and after that conversation, now I think he wants to do the alternate 1.5/3 spacing layout they recommended, but I'm not convinced that I should let them do it like that. Weedy, can you tell me how far apart your cables are spaced? Thanks everyone!

Clarification:

Your comment of "alternate spacing" lead me to believe that the first two cables would be spaced 3" apart, the next 1-1/2", the next 3", the next 1-1/2", etc.

I commented that rather than have that odd/even alternate spacing, I'd prefer an even 2-1/4" spacing all the way across the floor.

I either misunderstood you or you me. Regardless, sorry for the confusion!

With 1/4" tile the standard 3" spacing should suffice. This is comfort heating, not room heat.

Now if there is something about your installation that has the manufacturer recommending the 3"/1.5"/3"/1.5" alternate spacing, I'd ask why not just space them all 2-1/4" across the floor. It's the same amount of cable but with more even spacing. That's where I'm recommending 2-1/4" across the floor, as an "alternate" to their "alternate".

The strapping has notches that the cables go around. These notches are 1.5" apart. So, whether you are doing the spacing at 1.5"/3"/1.5"/3" all the way across the room or a uniform 3" all the way across the room, the installer can't make a spacing error since the notches act like pre-measured spacers. So, my guess as to why the manufacturer wouldn't recommend 2 1/4" spacing or any other spacing for that matter, is that it would not be idiotproof, as he'd have to manually measure the space between each one and there's room for error....it might not come out uniform. Keep in mind that the contractor's electrician who did the first uneven layout is the same guy that will be returning to do the new layout, but this time I will be there watching and commenting. What I'm trying to say is that I think this guy really needs for it to be as idiotproof as possible. That being said, do you think I would end up with hot and cold spots if I went with the manufacturer's recommendation of 1.5/3/1.5/3?

Yes, your floor will feel weird (i.e., not evenly warm) if you've got the alternating spacing. I've got one spot in my kitchen floor where the spacing of a single wire over a 3-foot length is a little wider than the rest (did it that way because of how I had to go around a cabinet), and every time I walk on it I can feel that it's colder.

The best plan would be to have 3" spacing throughout the whole floor.

Second best, if you can't shorten the wire (with the Warming Systems wire that we use you have to use the whole spool) would be to reduce the spacing uniformly throughout the floor to whatever it takes to use up the spool.

Third best, if you need to use up all the wire and want to keep with the standard spacing in the strapping, would be to go with 3" over part of the floor and 1.5" over the other part. Put the closer wires over the part you'll walk/stand on most (in front of the vanity). Then it's a half-and-half rather than a uniformly uneven (?) heat.

well, i respectfully disagree. I really really think that 1.5 + 3 + 1.5 + 3 + 1.5 + 3 + 1.5 + etc will even itself out well, but ... if you change it once in one area as in the small example above, you will notice a slight difference, and if you change it drastically as in the suggestion above, you will go from Zone A to Zone B and laugh every time at the temperature difference, and it'll be a conversation starter for every visitor. When the sun shines on an area it's normal to feel the heat so that's not a stun. If the sun shon only in one spot as it went overhead you would have the same "hot" area all day long; that'd be unusual but still understandable because of some weird roof line. If your floor has two zones that can never be adjusted independently, would you be satisfied? I would say to anyone asking about this, "you will not be satisfied with the resulting situation".

OTOH, I have put cables close together in the last 2" at a room's perimeter against an exterior wall, to give the floor more heat energy right where the cold is seeping in. I was satisfied with the end result.

HTH

p.s. never discuss heat cables with someone who talks about shortening the wire. They just don't have enough basic knowledge to be worth considering. The wire's length is the one thing that no-one can ever change. Unless they are as much an expert as the manufacturer is. Fixed wire length with a matched thermostat is the one reason why it is so hard to market this product. Otherwise you would be able to buy it in modular lengths and connect them as you expand your renovation project, bit by bit. You'd be able to mix and match and change your mind at any time. Like tile or drywall. Or like baseboard heaters that you can replace with smaller or bigger ones.

Thank you, David for your response. I'm glad you think my layout will probably be ok. I had sort of resigned myself to the idea that I would probably be unhappy, but now I have hope. The floor tiles are being installed as I type this (looks very nice so far). Soon as the heat is able to be tested, I will report back.