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Unread 07-21-2015, 08:47 PM   #1
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Ditra Heat wire length issues

First of all I like the Ditra heat system. I like the wire snapping right into the isolation membrane like it does and I think it's a great system. But, I wanted to see if anyone else has had the same issues I've had on a master bathroom floor. I installed a system that the contractor bought thru a local tile shop. The floor has two systems and two thermostats, one on his side and one on hers and both sides tie in together as one fairly large bathroom, nearly 300 sq ft. I installed the wires just like the instructions show, 3 studs apart and 3 studs away from the walls and cabinets, etc. When I got finished, I still had about 60 sq ft of floor without wire. We called Schluter to see if it was okay to spread the wire to 4 studs apart and they said no, has to be 3. Okay, so we ordered another cable for the rest of the floor and after covering it, we had 38 linar ft of wire left over.

We ended up using up the extra wire in a 2x8 closet. Not sure what we would have done if we wouldn't have had the closet.

I've installed many heated floor systems over the last 15 years or so. With other systems, I can remember installing the wires as close as 2 inches apart all the way to 5-6 inches apart which makes it easy to use up extra wire that's on the spool. But, when Schluter says 3 studs apart with the wire, not 2 studs, not 4 studs, it must be 3, how can we eat up any extra wire or vice versa? The wire has to be just the right length within a few ft looks to me like and I don't see that happening very often.

Has anyone else had this problem?

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Unread 07-21-2015, 09:03 PM   #2
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I was told by Schluter last year that I could go four apart but the floor would not warm up as quickly, I did and the customer has not complained about the floor...

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Unread 07-22-2015, 06:49 AM   #3
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I don't know about putting the wires closer together than specified, but placing them farther apart can't cause any problems.
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Unread 07-22-2015, 04:43 PM   #4
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Mr. Schluter says 3 studs apart. But other manufacturers that have told me I could use their cable in the Ditra Heat mat, said I could either do 2, 3 or 4 studs and would be covered under warranty (not Schluter's but theirs).
Isaac Ostrom
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Unread 07-22-2015, 06:50 PM   #5
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Isaac, what brand were the wires you used in the Ditra heat mat? I'd be willing to do the same if Schluter can't come up with a way to use up extra wire or stretch it when we're a little short. Or, come up with a way to get the exact wire length which would be hard to do every time.

Even when we called Schluter again, told them the exact sq ft we had and told them the length of the 3 cables we received, they said we had the correct length for that footage but yet we had 38 extra ft of wire left over with no way to eat it up besides tiling a closet too. This has wasted a lot of our time.

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Unread 07-22-2015, 07:53 PM   #6
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Do you plan out the runs by the linear feet that is listed on the box? To avoid having to pull them out and trying again I'll measure the runs and the returns and divide them into the lineal inches to see how close I get. Using longer runs uses more cable, I found.
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Unread 07-22-2015, 08:35 PM   #7
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If you can't vary the spacing, in the future try to always have an area(s) that will be optional for wire, like the sides & behind the toilet, or sometimes there is a square area next to the end of some cabinet layouts. Also you can vary the spacing away from the walls massively. Your shoulders only let you get your feet about 9" or 10" away from a side wall, and the wire will heat an extra 2", so that's a lot of leeway to vary the coverage. Also behind the door swing can sometimes be a foot or so from the wall and still get adequate heat where you need it. So next time under-order a little or at least plan at first on not putting wire in some of those areas, then use them as a buffer if needed.
I would also suggest ordering the wire based only the lineal feet measurement, and ignore their sq/ft recommendation. This lets you use your experience as a heat wire installer across all brands and spacing (keep good notes!), you'll have no one to blame but yourself.
The cool thing about Ditra Heat is that if you find your first layout doesn't work, it's very quick to just pull up all the wire and re-lay it based on some of the variables above, if you don't just have too much like in this case. I would sure recommend switching to another brand of wire (Suntouch is my favorite). Schluter is just unreasonable in their wire's instructions on a few areas. There's no way to perfectly meet their requirements.
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Unread 07-22-2015, 09:00 PM   #8
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I find ordering the next size down works well.You really need to measure well using the set backs for cabinets and floor registers.The system is great to install.

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Unread 07-23-2015, 12:39 AM   #9
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I've found that the wires don't go as far as the square footage says it does (surprise, surprise ) and that's on any brand. I found this out the hard way when I called the store thinking I must have got the wrong wire. Nope.

For those that come across this thread in the future I'll mention a couple of things to keep in mind:
The more turns that you have the more wire you eat up. The most efficient use of wire is big long runs

Like Tom said above, you always need to leave yourself an "out". You need to plan on where to run extra wire. The toilet closet is always a great place.

Don't ever vary the wire spacing in the floor. If your using a wire that isn't DitraHeat (because they won't let you vary the spacing) you can determine what spacing to run the wire. Don't run it at 2.5 inches and suddenly change to 3". I know a guy that had a costly tear out for doing this exact thing.
I do the opposite of what others have mentioned and I always over order the wire figuring that I'll run the extra out. I hate not having enough wire or not having certain spots heated. I can always run out 10 extra linear feet of wire.

Below is a photo of an old installation. It isn't DitraHeat. It's a Suntouch wire run with the cleats that I used to use some years ago. It's an example of what to do with the left over wire.

Name:  Running extra floor heat wire out.jpg
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Unread 07-23-2015, 06:05 AM   #10
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Thanks for the input guys, I appreciate it. The contractor on the job was trying to stick to Schluter's guidelines, they should know their product better than anyone. When I saw that 3 studs between the wires was going to run us short on wire, I pulled it up and snapped the wires in at 4 studs and just before I finished, the contractor called Schluter and they said that gaping at 4 studs is not recommended. That the tile floor would be cooler between the wires than it would be directly over the wires. I can see it being a little cooler but seems to me it wouldn't be noticeable to your feet.

I haven't given it much thought as to running long runs verses short runs or which way uses less or more wire. I figured it would be close to the same but I can't say.

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Unread 03-05-2016, 11:52 AM   #11
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shorten the cable?

is it a bad idea to just cut the extra cable off and cap off or seal the ends?
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Unread 03-05-2016, 12:10 PM   #12
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The way I typically do it is much along the lines of what Tom H. said. Run the cable approx 12 inches from the walls initially. then if there is extra cable I have room for an additional 2 runs along the whole perimeter. You just have to be logical about how the "escape route" is going to work.

But I hear your pain. It never seems to work out to the exact square footage on the box.
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Unread 03-05-2016, 12:13 PM   #13
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My only beef with E-heat is the way the membrane likes to curl up at the ends. I find I have to staple it down along the walls.
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Unread 03-05-2016, 01:36 PM   #14
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Originally Posted by JD
is it a bad idea to just cut the extra cable off and cap off or seal the ends?
Yes, not only is it a bad idea, it cannot be done without destroying the cable. A floor heating cable is manufactured to it's specific length, and contains a continuous circuit. To cut the end off, is to cut the continuous circuit off in the middle.
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Unread 03-06-2016, 01:07 AM   #15
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Cutting the wire causes the overall resistance to change, disrupting the designed current flow (sort of like putting a higher wattage bulb in a lamp). You need to keep in mind the maximum straight run on the wire given in the instructions as well (page 18 of the installation manual).
Jim DeBruycker
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Last edited by jadnashua; 03-06-2016 at 01:15 AM.
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