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Old 09-23-2009, 10:33 PM   #1
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Underfloor radiant electric heat


Hi

I am in Vancouver, Canada. My house has 3 1/2 feet crawl space. I gut out the existing tiles and going to install underlayment of 3/8" plywood over 1" plywood subfloor for porcelain tile installation. The main heating source is water baseboards. I am planning to put underfloor electric heat wire in entrance/hall(210 sq ft) way and kitchen (200 sq ft) as the floor gets cold during winter. There are some hot water baseboards in crawl space but they don't warm up the floor.

1) Is it a good idea in my situation?

2) Are mats better than cables? I am looking at heat cable rather than mat as I figured out that cable cost is roughly $3 per sq ft and mat cost is at least $6 per sq ft for material only.

3) Will heat cables or mats could cause any issue with stability of the tile floor down the road?

Thanks.
Arookie

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Old 09-24-2009, 01:22 AM   #2
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Underfloor radiant electric heat


dangdang--Approximately two years ago, my sister/husband in Atlanta, GA (certainly not your climate area) had a major remodel of their home done. One of the things they did was to have a "mat/grid" style of electric floor heating installed in their new 200+ sq. ft. master bath, and the new huge kitchen and dining area. There is tile in the bath and kitchen area on top of this "mat/grid" style heating system. Last winter was the test. It DOES NOT get as cold in Atlanta as Vancouver I'm sure, but the floors in these rooms were very cozy to the bare feet. I don't know anything about the electric cables used for underfloor heat to compare. These were sections of mats, 2' x 4' in size, they were cut to fit and somehow connected to each other. A thermostat controls the temp in each room. The bath are has a transformer to reduce the voltage from 110v AC to 24v DC (code) and works fine. NOTHING better than a warm floor after a long shower to me anyway. Just my 2 worth for you, David

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Old 09-24-2009, 01:57 AM   #3
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Underfloor radiant electric heat


I did a mat type one time in a smallish master bath. I did not really price wire vs. mat and it was many years ago anyway. Was a kit with mat, wall mounted controller, etc. It was installed under time. Worked great and sure was nice on those cold mornings!
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Old 09-24-2009, 07:38 AM   #4
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Underfloor radiant electric heat


I think the advantage to the mats is that some brands will make it to the footprint of your room so you can just unroll it instead of manually laying it out.

Whichever way you decide to go check the resistance before install and several times after that before the tile is installed.
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Old 09-24-2009, 08:48 AM   #5
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Underfloor radiant electric heat


An alternative would be to just add one or two "zones to your existing hot-water heating system. You say you are going to put down a 3/8" tile underlayment, so cut that underlayment into 7-3/4" long strips and run 3/8" HEPEX tubing back and forth over the desired heating area with the 7-3/4 strips between them. Where the tube curves around for the next run just cut a piece of underlayment to fit inside and outside of that curve. The tile mud or mastic can be applied directly to the underlayment surface and also lightly troweled into the crevices around the tubing. Since 3/8 tubing has the same 12" radiation pattern as the larger 1/2 tubing if you lay it on 8" centers there will never be any cool and warm stripes across the floor. You don't want to run more than 140 DEG (F) water in the floor, but it will still be toasty everywhere on the tile.
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Old 09-25-2009, 02:09 PM   #6
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Underfloor radiant electric heat


Thats another great idea but I am not sure if it is possible to add another zone in existing house, it may require lot of expensive labor to do that.

I have no idea but is it possible to utilize existing zone as I have 1/2" piping going around in crawl space which I can extend and connect 3/8" pipe and lay it out in kitchen and entrance hall way. Can I cut 1/4" inch tile backer or Ditra XL membrane and layout pipes between it and then install tiles on top of it.

Please suggest.

Thanks.
Arookie
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Old 09-25-2009, 04:30 PM   #7
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Underfloor radiant electric heat


I definitely would not recommend tying your "Floor Warming" to your "Room Heat" circuits. The first reason is that your radiators in your rooms and the loop(s) in the crawl space are operating at 180 DEG (F). The floor warming, as I said before, only operates at a maximum of 140 DEG (F) down to as low as 100 DEG (F) to prevent cracking of the tiled surface, and to cut down on the expansion of the HEPEX
tubing and so as to not burn someones tootsies. I suppose it could be done by a credible plumber/boilerman if you added a tempering valve in-line with the loop for your floor assuming you have a two-pipe system either for your crawl space or for the intended room. If all your radiators are in one continuos loop you have a one-pipe system (I.E. one thermostat). More than one thermostat usually means a two-pipe system. If you do decide to tie into the crawl space or the intended room's radiator line be aware that the floor will be heated only when the room heating is working and for as long as it is calling for heat so your floor could be cold when the room is comfortable or it could be as hot as the sands of the Sahara for as long as the T-stat calls for heat. Just some things to think about. Plus if you are putting down 3/8 underlayment why do you want to put down another 1/4" layer under the tile. The only reason for all those layers would be to level the floor with the adjoining floors.
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Old 09-25-2009, 04:37 PM   #8
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Underfloor radiant electric heat


Electric heat can be more expensive, so adding a zone might be worth it in the long run

I went with electric cable, small bathroom - unheated but sandwiched between 2 heated rooms
It has an exterior wall - better insulated then the rest of the house

For the same prices as a matt I bought enough cable to do the bathroom outside of the hallway & part of the long hallway
A warm floor is really nice, especially a tiled one as that will feel colder !!
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Old 09-25-2009, 05:01 PM   #9
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Underfloor radiant electric heat


Ask the vendor how they recommend that anyone find a break in the system without tearing up the whole floor.
Check if their recommendation is credible/reliable/etc. and not so expensive that you might as well tear up the whole floor.

It helps if the system is at least somewhat tolerant of somewhat improper installation, and tolerant of the normal stuff that shows up as a house ages.

Last edited by Yoyizit; 09-25-2009 at 05:04 PM.
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Old 09-26-2009, 11:49 AM   #10
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Underfloor radiant electric heat


Thanks everybody for the reply.

I will ask my plumber how much it may cost to add a zone and layout the pipes for radiant heat and compare the cost to lay out electric heat. I am not sure how to compare the usage cost but generally hot water radiant heat is cheaper to run.

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