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Subject:  Re: Radiant Heat System Date:  1/7/2004  9:18 AM
Author:  Goofyhoofy Number:  44334 of 138082

The in-floor radiant heated homes that I've been in had the pipes buried in concrete floors (and generally, where carpet was laid, didn't even have a pad between the concrete and carpet to enable better heating - plus probably not as much concern should a pipe spring a leak.) I couldn't tell in the photos. Is your house built on a slab, perchance?

No, the house has a full basement, this bathroom is on the first floor, over a basement bedroom, closet, and utility closet.

There is no way I could have put in a layer of concrete (or other) subfloor to encase the pipes without raising the level of the floor by several inches. (And if you don't raise it enough, the heat won't diffuse to the areas between the pipes enough to prevent what's called "striping", where the heat alternates with cold stripes in the floor. In a similar way, I suffer the same fate because I didn't go on the "tub side" of the joist next to the tub, and have a "cold stripe" about 6 inches wide next to the tub, as I detail on the website. My fault, I should have known better.)

Anyway, I got much of the mechanics of the "below joist" system from a commercial system called "Ultra-Fin" (, which they sell as both a construction and an after-market (retrofit) product. It goes between the floor joists and warms the air, which warms the subfloor, which warms the tile.

They want to sell the whole shebang, including boiler, etc. for several thousand dollars and I was trying to avoid all of that by just pulling hot water from the house system, but it wasn't enough. I ended up with a cheap and small hot water tank ($130 at HD) under the sink, which does the job very well indeed. Total cost was about $350 for the flooring materials and maybe another $350 for the entire "heating system."

I will say that the Ultra-Fin system looks pretty slick (and found their PDF instruction manual particularly helpful), but I elected to run pipes parallel to the joists rather than perpendicular to them because it was easier, to use copper rather than PEX because I thought it would bleed the heat better, and to do a lot of other things as I "invented" my system. It was great fun!

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