View Full Version : Radiant Floor

Bob Winkler
08-09-2005, 7:43 AM
I'm converting a screen porch at my daughter's house to a permanent, 4-season den. All the walls, windows and slider are framed and I'm beginning the inside work now. The porch is built on concrete slab and has existing ceramic tile floor.

I plan on installing a hot air register to bring heat to this room. My daughter is insisting on new ceramic tile, and my concern is that the floor, being on slab, will be COLD. It gets pretty cold in New England. So, I'm considering embedding electric radiant mat in the thinset used for the new tile. It seems pretty popular and not too difficult to install.

Does anyone here have any experience with electric radiant heat? My concern is that the thermal mass of the slab will be a giant heat sink, and the radiant heat will have little or no effect. Any input at all would be really appreciated.


Ken Fitzgerald
08-09-2005, 7:56 AM
Bob.....the heat sink theory/thermal mass will work both ways. Once heated it will hold the heat longer and decrease the drop in heat. I did a lot of research on radiant floor heat for my shop. Google on radiant floor heat. There are a several companies out there that provide valuable information about using radiant floor heat and design considerations. Good luck with your decision!

John Hart
08-09-2005, 8:02 AM
I'm posting so I can monitor this thread Bob. I've been wanting to do this to our Screened porch as well and couldn't decide whether to pump furnace air out there or heat the floor. Maybe I'll learn something.:rolleyes: Then again....Maybe I'm unable to learn.

Bill Lewis
08-09-2005, 12:53 PM
My only experience is that we have it in our master bathroom. The only thing I would have probably done differently would have been to use the 240V version vs. the 120V version. I think it would heat up quicker. Also, from my experience with the electric system, I wouldn't rely on it being able to heat the whole room, just take the chill off of the floor. So you are correct in adding the furnace vent to the space.

To be efficient, I still think you would need some sort of thermal break from the slab. Yes the slab works like a big thermal mass, but so does the grade below, which could suck the heat out, which is one of your concerns.

My neighbor installed a hydronic radiant floor system in his house (rare around here) and was required to put 1/2" foam board insulation beneath the basement slab.

Bob Winkler
08-09-2005, 12:57 PM
That's exactly what I was worried about- heating up the whole earth and paying out the nose for it:eek:.

The thermal break makes sense, but may be impossible in my situation without raising the floor too musch.


Frank Hagan
08-10-2005, 1:55 AM
Actually, a tile floor may feel colder, but a tile and wood floor would be the same temperature. The difference in feel is the amount of conduction of heat away from you ... tile conducts it better than wood. Carpet, with foam padding, actually provides some insulation. A throw rug is a good compromise; it will be the same temperature as the tile, but it feels warmer because it doesn't conduct your body heat away from you.

Electric radiant may work differently than hydronic heat buried in a slab. The coils are just a half inch away from the surface of the tile, and if its a poured slab, the area beneath the coils is probably 3 1/2" thick of what will be thermal mass. Check with the manufacturer, but I suspect you won't lose much heat down through the slab. You are just taking the chill off the floor, not trying to heat the entire room with it.

Jeff Sudmeier
08-10-2005, 9:06 AM
When one of my friends decided to put radiant heat in his shop, he was told to lay down 2 inch foam, before the creete to help slow the heat loss.

I don't know the difference that having the radiant heat above the slab will do, I would make a call to the manufacturer and find out what they suggest.