Bathroom floor heating

[rktinc]

I just bought a 9500 sq foot building. The 100 year old walls are solid brick, the ceiling is well insulated. the interior temp has stayed around 40 even though day time exterior temps have gotten in the 60's recently. The building is unheated at this time and sat empty all winter with no damage to exposed pipes. The bathrooms have NOT frozen at all. I am considering buying a small electric floor heating mat to put under new tile when I restore the two small restrooms.

My goal is to set the temp to 40 degrees and only use it when temps get extreme which is rare in southern Kansas. Any thoughts on why this would not be a good alternative for a storage building / shop?

I can't imagine electric use being high with a 24"x48" 120v floor pad.



Thanks,

RKTINC

 

[PoorUB]

You will not get much heat from and electric floor heating that size.

I have tile floor in my bathroom and put an electric floor heat mat under the tile. The mat is roughly 3 feet x 10 feet. We run the floor temp around 82F. I have closed the bathroom door over night just to see what happens to the room temp and in the morning it doesn't feel any different. I expected it to be hot in the morning. I suppose I could turn the floor temp up higher, but 82F seems comfortable. Perhaps at 90-95 degrees it would heat the space.

Also I have wood floor. Your heating mat will heat down into the concrete too.

The mat I put in was 12 watts per square foot.

If you are concerned about freeze up, a wall heater or baseboard strip will do better.

 

[NWOhioChevyGuy]

Doing a bathroom addition currently that will have in floor electric under tiles and I'm planning to use this system w/ the Prodeso decoupling mat. Order the wire to the floor size and "custom" make your heating element to the space.

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Like PoorUB Mine will be on a wood subfloor over a crawl space.

 

[duneslider]

Those floor mats under tile really don't do much more than give you a warm floor for you feet to stand on. They just don't radiate that much heat. Typically, the thermostat associated with the floor heat is to check the temp of the floor, not the air in the room. So, once the floor sensor reaches the set point it turns off until it drops then comes back on. The air above it could be 60 degrees, or 40 and it doesn't care it will turn off when the floor is to temp. They are sold more as a luxury item so toes don't get cold standing on cold tile.

You might be better off with an electric baseboard heater or a wall/ceiling mounted radiant panel.

 

[PoorUB]

Those floor mats under tile really don't do much more than give you a warm floor for you feet to stand on. They just don't radiate that much heat. Typically, the thermostat associated with the floor heat is to check the temp of the floor, not the air in the room. So, once the floor sensor reaches the set point it turns off until it drops then comes back on. The air above it could be 60 degrees, or 40 and it doesn't care it will turn off when the floor is to temp. They are sold more as a luxury item so toes don't get cold standing on cold tile.

You might be better off with an electric baseboard heater or a wall/ceiling mounted radiant panel.

I have to wonder, it shouldn't matter. With hydronic radiant floor you will run the floor temp just a few degrees above the room temp, so why doesn't an 80F floor heat the room with electric mats. It should, but my experience says it doesn't.

Cripes, the 12 watts per square foot works out to 40 BTU per square foot. We were going 15 BTU per square foot on other heat sources in newer homes. It should heat the space easily if you have enough square feet available.

Either way you need to pretty much cover the available floor surface, not just a few feet in the middle of the floor.

 

[duneslider]

I have to wonder, it shouldn't matter. With hydronic radiant floor you will run the floor temp just a few degrees above the room temp, so why doesn't an 80F floor heat the room with electric mats. It should, but my experience says it doesn't.

Cripes, the 12 watts per square foot works out to 40 BTU per square foot. We were going 15 BTU per square foot on other heat sources in newer homes. It should heat the space easily if you have enough square feet available.

Either way you need to pretty much cover the available floor surface, not just a few feet in the middle of the floor.

Most Floor heat I have done has a temp sensor embedded in the thinset on the floor, so it turns off as soon as the floor temp hits the correct temp. Hydronic Radiant floor heat has a temp sensor on the wall watching the air temp and not the floor temp so it keeps running until the air temp rises. Most floor heat mats are not sold to heat the room but just to heat the floor. I have never done a tile floor mat type system that did anything but warm the tile. I have noticed that rooms with the tile mats generally "feel" warmer due to the radiant effect of the floor but the air temp isn't any different.

 

[PoorUB]

Most Floor heat I have done has a temp sensor embedded in the thinset on the floor, so it turns off as soon as the floor temp hits the correct temp. Hydronic Radiant floor heat has a temp sensor on the wall watching the air temp and not the floor temp so it keeps running until the air temp rises. Most floor heat mats are not sold to heat the room but just to heat the floor. I have never done a tile floor mat type system that did anything but warm the tile. I have noticed that rooms with the tile mats generally "feel" warmer due to the radiant effect of the floor but the air temp isn't any different.

I understand, but whether you heat the floor to 80F with water tubing or electric mats, where is the difference? The floor is 80F either way, it should heat the space either way.

 

[rktinc]

All good information. I did not know the sensor was imbedded in the floor. That would make sense as to limited air temp changes. Back to the drawing board.

 

[Showkey]

Heated bath floors is comfort thing. Generally they are warm the touch 78-85* F.

In a very well insulated home example R50-R60.
120 sqft heated bath floor heated with the in floor heat at 80* will warm the entire room. Obviously the bath will not be 80*. The attached bedroom will be warmed slightly from the bath convection.

Freeze control could be handled by a 120v line thermostat set at 40* and small electric heater.