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Subject:  Re: Radiant Heat System Date:  1/8/2004  8:01 AM
Author:  Goofyhoofy Number:  44370 of 135495

I was trying to avoid all of that by just pulling hot water from the house system, but it wasn't enough.

Could you elaborate on why it "wasn't enough"?

It didn't warm the tiles enough for my taste. The original Auto-Circ pump has an on-off cycle between 95-85 degrees, respectively. That cycled about every 20 minutes when I had the HWH at 125 degrees. I raised the HWH to 135 degrees, and the cycle moved back to about every 30 mintes. (Hotter water did get in the pipe [although there was a mix-down for the first 5-10 feet, that was always cooler] but raising the temperature just increased the amount of time before it hit the 'start-up' cycle again.)

Perhaps it would have worked with the "Ultra-Fins", but the PEX pipe they use doesn't bleed heat as well as copper, so perhaps it's a wash. (Perhaps not, I have no way of knowing.) I chose the copper pipe because the layout was weird, (it's an L shape with a 45 degree bend at the junction) the Ultra-Fin system goes perpendicular to the joists and it seemed easier to run with the joists for me. (Also, because I do some metal sculpture, and have done a lot of plumbing, I'm very comfortable with sweat fittings & soldering & so forth.)

It looks like one could simply run that Ultra-Fin stuff using a recirc pump off the house's water heater. You might need a bigger water heater (or a second heater) than you would ordinarily need, since the Ultra-Fins would be using some of the capacity, but it seems like it would be cheaper and simpler than a seperate boiler

That was the original plan. In fact when the original AutoCirc didn't provide enough heat, I got one which they said was "variable", but only the "turn back on" component was variable. So it always shut off at 95, even though I could get the "back on" temperature at 91, increasing the frequency of the cycling, but it still wasn't enough. So I got their 909 model (works with higher temperatures, but does not provide the sink connections) and closed the loop with the $130 undersink HWH.

The application I'm thinking of is just heating the tile floor of a master bathroom up some — not actually trying to heat rooms, just make the floor feel warmer.

Me too. With the room temperature at 70, the original AutoCirc got the tiles up to 74, and it "wasn't enough". With the 909 pump I did increments until they got to "enough", and found - for my taste - it was at about 83 degrees ( by driving the water at 140, and the pump cycles at 140/130). What is true, however, is that at 83 and the room at 70, they give off their ambient heat and "heat the room", so I shut off the forced air vent feeding the room.

My trick now is to get those friends who are interested in the project to feel the tiles where there is no heat (linen closet, the cold stripe next to the tub, aarg) and where there is. Invariably the response is "Wow, that's cold" and "Wow, that's comfortable." The temps are 70 and 83, respectively.

One last note: I did find a buildup of heat in the vanity under the sink (to about 90) because of the HWH which I defeated by raising the countertop the height of a nickel (by using a few nickels!) and putting a small air vent near the bottom. Now the sink basin/countertop is "comfortable to the touch" but the cavity undersink runs about 79 degrees. That helps heat the room too, of course.
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