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aak3 01-27-2008 09:29 PM

porcelain tile over electric radiant heat
I am remodeling my kitchen. My current floor is made of 3'' wide strips of T&G hardwood that is 3/4'' thick. Overall it is in pretty good condition but not quite good enough to salvage as the main flooring. It is splintering more and more, the T&G are starting to separate and my wife doesn't feel the floor can be cleaned all that well. There is no sub-floor beneath the strips so they are attached directly to the joists (13'' oc) which are in great condition given their age (100 yo). I want to disconnect the radiator in the room and put electric radiant heat underneath some 12x12 porcelain tiles. So I have a couple of questions:

At 3/4'' thick, will the hardwood strips be thick enough to lay the cement backerboard on, or should I put OSD between the two? That would make 1.5'' of sub-floor, which would cause a significant bump between the kitchen floor and the dining room floor.

Because I will only put the radiant heat under the exposed tile, do I need to put anything under the tile that isn't heated to make up for the 1/8" thickness of the heating mats? I will tile under all the appliances, but should I/do I even need to tile under the cabinets?

Thanks for any input

redline 01-28-2008 01:13 PM

How cold does it get in your area?

aak3 01-28-2008 05:38 PM

We live in Washington DC. We get below freezing a couple times each winter, but usually low 40s to mid 30s. The kitchen faces to the north so not a lot of winter time sun in the room.

JazMan 01-28-2008 07:29 PM

Hi Kurt,

First of all you have the wrong idea on what the electric mats will do. They are intended to warm the surface for your bare feet few hours a day, not to provide heat to the room. Keep the radiator, you need it.

You can NOT install tile backer board over any plank flooring with a high degree of success. Even adding another subfloor over it before the backer isn't a recommended procedure. So, remove the old subfloor and start with new 3/4" t&g plywood subfloor. You can then install the backer or a product such as Ditra matting and then the ceramic tiles.

Before you go any further though, and considering the age of your house, we need to know the spec of the joists, do you know the species, grade, size, spacing and the unsupported span? While under there, inspect if in good condition or not.


aak3 01-28-2008 09:00 PM

Thanks for the reply. I don't know the species (maybe spruce...they have a dusty white coating on them that makes it hard to tell right now) nor the grade of the joist, but they are true 2x10s that are spaced 13''oc. They look in very good condition and run the width of the 14ft wide kitchen. I assumed that replacing the planks with new sub-flooring was the correct answer but I just wanted to make sure that I wasn't wasting money needlessly. This will also give me a perfect chance to check all the plumbing and electrical wiring under the main floor.
Your comment about the electrical mats blindsided me. I have read in many websites, including the Radiant Panel Association, that under floor electrical radiant heat could be used:
1. Floor warming; eliminate those cold bathroom or entry floors, warm up cold tile or chilly wood floors
2. Space heating; as the primary heating system for a room, house or commercial building
3. Spot (zone) heating; apply heating to specific areas with individual control.

I have relatives in PA which use a hydronic system as their sole heating source in a MUCH larger kitchen than mine. My kitchen is only around 174 sq ft and I planned on using around 125 sq ft of mats. I know you can get 120/240v systems but I didn't think that was even an issue. Are you thinking about your conditions up in MI with the harsher conditions? I was ready to pull the trigger on this but you have stopped me in my tracks?!?!


Bud Cline 01-29-2008 11:18 PM

Kurt the radiant heat on the market today for heating tile floors WILL NOT heat a room space. :no: They are intended to only take a chill off of a tile floor and no more. Supplemental heat is always required :yes: to heat a room that is also using those heating systems.:)

aak3 01-30-2008 06:31 AM

Thanks...I guess I will keep the original heat as well.


Bud Cline 01-30-2008 08:33 AM

Good plan!:)

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