Large heated tile floor

kwired

Electron manager
Location
NE Nebraska
Apparently a lot, they are still figuring :)

I can tell you it will depend on watt density you end up installing. Then voltage comes to play as well, can get twice out of a 20 amp circuit @ 240 than you can at 120.
 

Barbqranch

Senior Member
Location
Arcata, CA
Occupation
Plant maintenance electrician Semi-retired
A quick Google check indicates 15 watts per square foot is a common upper limit for design.
 

kwired

Electron manager
Location
NE Nebraska
A quick Google check indicates 15 watts per square foot is a common upper limit for design.
10.5kW for a 700 square foot room is a lot of heat. I'd think keeping it down to 2 to 3 kW would be plenty unless maybe it is the only heat for the space, but even then maybe up to 5k would likely be fine. Don't want to have to wear oven mitts on your feet to walk on that floor:cool:
 

Barbqranch

Senior Member
Location
Arcata, CA
Occupation
Plant maintenance electrician Semi-retired
When I built my house and had floor heat in the bathroom, there really wasn't any choice in watts per square foot, the mats were all the same per foot, just different sizes. If it is the type w/ a heating wire laid out on a grid, they might be able to adjust it, but there are standard ways to do these, and it isn't really in the electrician's ability to choose it. It is up to the tile layer and the owner.
 

retirede

Senior Member
Location
Illinois
When I built my house and had floor heat in the bathroom, there really wasn't any choice in watts per square foot, the mats were all the same per foot, just different sizes. If it is the type w/ a heating wire laid out on a grid, they might be able to adjust it, but there are standard ways to do these, and it isn't really in the electrician's ability to choose it. It is up to the tile layer and the owner.
I have Suntouch brand in my house. They are 12W per sqft. And every square foot of tile doesn’t normally get mat under it, especially if the room has an irregular shape. Actual installed density is likely closer to 10W per sqft.
 

James L

Senior Member
Location
Kansas Cty, Mo, USA
Occupation
Electrician
At 240v it's 1 amp for every 20 square feet, or 12 watts per sq ft.

I've put in kits as large as 8 amps, which was 160 sq ft

You can add slave units off of the thermostat to add larger systems.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
You will probably need 2 - 20 amp cir. Danfoss catalog shows there largest unit doing 210 sq.ft and draws 8 amps. You can use 2 of these on one circuit. The problem is the T-stat won't handle that much load... You could use 4 T-stat--yuck
 

mkgrady

Senior Member
Location
Massachusetts
Typically for these larger systems you would get a relay module(s) that you mount in a box(s) by the floor and the tstat controls those. I needed 4 on a recent job because each loop was slightly over half a circuit.
I believe the testator also proves the gfci protection. If the stat is just pulling in a relay that powers the heat how do you get the gfci protection? I guess the branch breakers. Any down side to that? You will not a a trip indicator at the tstat.
 
The customer just changed to non heated wood floor, thankfully. Another room 400 sqft will be heated tile but that’s much easier. You were probably right about Louisville Tile not answering my calls, probably not knowing what to recommend. Thank you.
 
A Schluter rep told me for that size room (20x20) I need a thermostat coupled with a power module. ( 2) 240v circuits, one to the tstat and one to the power module with a low voltage line between the two. The module doesn't have to be on the wall, can be in closet or crawlspace. I've never installed a heated floor with such a module.
 

James L

Senior Member
Location
Kansas Cty, Mo, USA
Occupation
Electrician
A Schluter rep told me for that size room (20x20) I need a thermostat coupled with a power module. ( 2) 240v circuits, one to the tstat and one to the power module with a low voltage line between the two. The module doesn't have to be on the wall, can be in closet or crawlspace. I've never installed a heated floor with such a module.
It's easy. It will have a line-in and line-out just the same. And there will be small contacts to connect the control wire, the same way you would connect the sensor wire.

I used the same kind of setup in a different brand, where the main thermostat was in the wall and I had two of the slave unit relays in a crawl space. I had 2 kits that were 240 volts and one kit that was 120 volts, so I was forced to use the relay system
 
Top