Replies

1. 
   Guest_ | Mar 30, 1999 08:14pm | #1

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   I agree on the reasons you prefer metal plates between the studs. I don't have actual experience with radiant floor heating, but I can offer my conceptual thoughts from a broad knowledge of engineering.

   If heat transfer wasn't an issue, then most people would probably prefer the "under-floor" installation. However, heat transfer IS a BIG issue, especially if you want wood flooring or carpet. By placing the tubes UNDER the floor, the heat must be conducted through an extra 3/4" of wood subfloor. That extra thickness of wood will insulate more than you'd suspect, requiring the water in the system to be hotter in order for the final finished floor surface temperature to be the same.

   There are some BENEFITS to a thin-slab floor, including sound silencing (the old submariner in me coming out) and fewer floor vibrations due to common household traffic. If your power goes out for a significant length of time, the extra thermal mass will result in a slower interior temperature rate of decrease.

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   Guest_ | Mar 30, 1999 08:21pm | #2

   *How do you install carpeting over a thin-slab concrete or gypsum radiant floor? I understand that it will provide unwanted insulating effect, but let's say I still insist on having some radiant-floors carpeted. What's the best way to fasten the tack-strips around the perimeter? Is there a certain brand or type of carpet that works better? I would guess that a Berber carpet would be better than a thick plush carpet, mostly because a Berber is thinner.

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   Greg_B_ | Mar 31, 1999 12:05am | #3

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   Except for the basement slab, I have all my tubing under the subfloor and it works fine. Whether it's in a slab or not, most houses with radiant floors will have areas with carpet and pad, which has a lot more R value than 3/4" wood subfloor. The key to heating through insulative materials is to provide at least twice as much insulation underneath the tubing as what's over it. I use foil faced R11 FG with the foil towards the tubing but not touching, and skip those metal plates, they're noisy. The bats also help with sound transmission from above. Greg

3. 
   Scott_Lewis | Mar 31, 1999 12:05am | #4

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   I would like to know how hydronic radiant floor heating systems in light-weight concrete slabs atop subfloors compare with those between the joists on the undersides of subfloors in terms of heating performance and energy efficiency. My intuition is that slab systems would tend to perform better because of the heat absorbent quality of the concrete. From purely a design point of view, however, I would prefer the between-the-joist system because it could be easily monitored and repaired, because it would not involve the additional weight load that a slab would, and because there could be no slab failure. I would appreciate the comments of anyone who has experience with both of these kinds of hydronic radiant floor heating systems. Thanks.