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Subject:  Re: Radiant Heat System Date:  1/7/2004  3:48 PM
Author:  Goofyhoofy Number:  44359 of 135480

Note that the Ultra-Fin system uses fins for the heat transfer, not the pipe.

That's quite true, I'm just not sure if it's important.

The Ultra-Fin system wants a boiler running water at 160 to 180 degrees. I'm running a hot water heater at 140 degrees and it's providing sufficient heat. The fins would certainly help pull the heat out of the pipe (although their system uses PEX, not copper, so I suspect I have a fair amount of "heat radiating surface" that PEX doesn't match, inch for inch) and diffuse it evenly in the stud cavity.

OTOH, I set the piping away from the stud by 3/16 inch to allow air flow. Putting it next to the stud would have made the bottom quarter of the pipe ineffectual, a stagnant quadrant anchored to the wood. By moving it out, I hoped to get a little Bermoulli principle going, the heated air would rise faster in the confined space, causing air movement thoughout the stud cavity to some small degree, evening out the heat distribution. I don't know if it works that way, because I can't get back in there to measure, but the minor differences in floor temperature do not seem to correlate with the locations of the pipe runs, so perhaps it does help, or perhaps it wasn't important in the first place. Dunno. It didn't cost anything to do, so I did it.

At any rate, the "fins" would help draw more heat out of the pipe more quickly, which I don't need to do, and to even out the distribution, which I don't need to do. (The estimated cost of running the Laing pump is about $3.00 per year. I don't really care how much it runs.)

Frankly, I don't know why heating a "thermal mass" is going to be a lot more efficient than heating a sealed air space, but perhaps it is. The way I figure it (which could be wrong), I am heating "x" amount of water, which runs out at 140 and back into the heater at 130 to be reheated to 140. If I had the "fins" I could run it out at 140, wait til it dropped to 120, then run it back and heat it back to 140. Where is the savings? Why does the ultra-fin system want water at 160-180 through a thousand dollar boiler, but 140 water with a $130 heater works for me? I would be curious to know how this is worse.

I think I read somewhere that you can seal the floor cavity and insulate/put something reflective on the bottom.

The floor cavity is "sort of" sealed; it has drywall below and subfloor, mortar, concrete board, mortar, and tile and grout above. That's pretty sealed. However I have had several people recommend that I put a piece of reflective insulation on top of the roll insulation next time, so perhaps I will do that. (I note that the Ultra-Fin folks recommend that only instead of the roll insulation if the stud cavity is 6", and I had 12" studs to work with.)

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