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Old 10-27-2012, 02:21 PM   #1
Magnum TI
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Location: Portland, OR
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Large area heated floor

My general contractor wants me to bid on a 225 sf heated bathroom floor.
I have never installed floor heating over 100 sf, and I am wondering if there are 225 (or so) square foot units available that come on spools. I imagine I can also use heating mats, but is there anything I should watch out for since this is a much larger area?

The floor will be travertine 18's on a diagonal.

Also - if I start with a 1 & 1/4" plywood subfloor, what do you folks recommend to use to install the heating, then the travertine? Since trav is so brittle, should I install something like Ditra under it, or is that not necessary?


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Old 10-27-2012, 03:25 PM   #2
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First you need to check deflection for natural stone. Then if you can go with 220v you can get close with Warm Wire. If 110v you will have to use multiple wire but can use same thermostat. Here in Portland you will also need a permit for install. In multnomah and clackamas county you need 2 conduit lines from box. 1 for wire and 1 for thermostat. I install WW directly on plywood as per instructions. DONT GET TO CLOSE TO TOILET. Then prime floor pour SLC Ardex GS-4 over wire then apply Ardex 8+9 before tile install.
If you've never installed thats a big floor to practice on. Good Luck.
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Old 10-27-2012, 03:32 PM   #3
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Suntouch warmwire has a 240 vac model that would give you 200 sq ft heated floor area at 2 1/2 spacing.
I would go cbu, warmwire, then slc. I suppose ditra would work, but I prefer cbu.

Model number of the warmwire is 240200wd
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Old 10-27-2012, 09:31 PM   #4
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We us flextherm heating systems up here.. which I believe are also available to you in your areas - best warranty
process : install heat system - self level - ditra over top - install travertine
flextherm systems at 240 volt can get systems to cover 264 sq ft at 4" spacing and now 3 watt system list is aprox 1300.00 - thermostat aprox 200.00 you may get it cheaper down there
you can join heat matts upto 2200 watts per thermostat
or have the heat matt company make up one to fit the area you are covering..this way you have better coverage through out and no coldspots between mats.. when special order like this , usually 2 weeks leed time and aprox $15 to $20 per sq ft to custom make..(easier install, more money to purchase) and even if you buy 2 heat matts you will be more pricier then one strung wire...
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Old 10-27-2012, 11:31 PM   #5
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I have done a couple that were in the 400 sq ft range. 2 wires and 1 thermostat, let the electrician figure it out. Around here Nuheat and Flextherm are popular. I would install the wire on the plywood per manufacturer guidelines and skim with thinset. I prefer thinset, because it's 1/3 the price of SLC and I can get it done just as fast. All thinset's I use are approver for 1/8" skim, and that's all you need if you recess the probe and splices. The trick is not to mix the thinset any thinner than you would for setting tile and use an 18 inch trowel, sand off high spots the next day.

Cover with ditra, or whatever antifracture membrane you like. Redgard, or greenskin would also work. Leave 1/4 inch for expansion at the perimeter.
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Old 11-02-2012, 06:52 PM   #6
Magnum TI
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Thanks for the replies!

maybe I will skim coat the wires with thinset and a plastic trowel, but if I use SLC, what is "Ardex 8+ 9?"

Thanks again!
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