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Subject:  Re: Radiant Heat System Date:  1/9/2004  9:26 AM
Author:  Goofyhoofy Number:  44412 of 137218

Note to other board members: I was going to just e-mail this to Radish, but decided against it, since "Radiant Heat" does come up from time to time and this might be a good thread for others thinking about a DIY installation in the future. . If this thread is getting too arcane (which I suspect) hit the "Ignore Thread" option and just ignore us.

Fins should let you use cooler water or faster-moving water, or both, and still get the same BTU transfer per unit time. Whether that's an advantage or not would depend on your circumstances.

Agreed. But if you have "enough" then you don't need "more" to make the transfer. And generic copper pipe is a lot cheaper than fancy schmancy, eh? And if you have "enough" you can dial it up or down at the source (the heater) or elsewhere (the pump).

OK, as I was sitting down a few moments ago (too much information alert) I realized that I had missed, or rather ignored, an important part of your scheme. Which is that you are going to drive it off a home hot water heater, presumably at lower temperature than I use (probably 120 or so versus my 140.) And therefore you need to pull more of the heat out of the pipes faster and move the water more often to accomplish that.

I did a fair amount of [very] subjective testing before I closed up the floor, since I couldn't do anything after the fact. I found that the pipes "gave up" their heat in a 20 minute cycle or so - close to, but not identical with the pump cycle, and that the temperature fell at a fairly constant rate thoughout that cycle. My method of measurement was "gripping the pipe with my hand", so you can take the precision of my statement with a large grain of salt.

I would say that the last 3-5 minutes the heat was back around "normal" ambient temperature, which is why I thought the first "adjustable" model might make enough difference (switch back on at 91 instead of 85, and therefore cycle a bit more frequently.) It did cycle more frequently but didn't make enough difference. And as you correctly point out (and which I didn't get from your post at first), drawing heat out of the pipes faster would do no good if the thermostat in the pump didn't recognize that. Got it.

When I switched to the 909, I could have merely raised the temperature on/off parameters to above the actual maximum water temperature and it would have run continuously and forever, right? But since I didn't have a recirc line (as you will), I didn't want water that hot flooding the cold water lines for fear of scalding, even with my protective reservoir.

Anyway, I now "get" why you may want to build the system in components, although I still believe you could accomplish the same goal with an integrated system, set above the temperature threshold and dialed back when you find your optimum temperature. I'll admit that is a bit of a kludge, but then I like have one replacable part rather than three, wired together.

OK. I'm on the same page. Finally. I think. Maybe.

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