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Subject:  Re: Radiant Heat System Date:  1/8/2004  9:06 PM
Author:  Radish Number:  44396 of 137308


My thought is that once I find out how long (and what diameter) the hot water piping is, I can look up the expected rate of heat loss. — Radish

Unless you have a lot of experience with this and similar HVAC stuff, I will guess that whatever number you come up with will be wildly wrong because of things which you do not anticipate.

I have charts, "Heat Loss From Horizontal Tarnished Type K Copper Tubing" and "Heat Losses From Covered Pipe" that should get me in the general vicinity, except for elbows and other fittings.

I figured I needed a certain number of BTU's to be produced and a certain number of BTU's transferred under the floor. I didn't see how the "fins" would change that equation, except to disseminate the heat more evenly, which I didn't think a problem (and turned out not to be.)

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.

I expect this will be a small number, and that a very small pump could simply run continuously (rather than being thermostatically controlled, like the Auto-Circ models). — Radish

I don't understand why that's preferable, but OK.

For a number of unimportant reasons. One, the Auto-Circ scheme assumes the water at the pump (when the pump isn't running) loses heat at the same rate as the pipes in the house, which probably isn't true (especially if the pump is located near the water heater in an unheated space, like mine will be). Two, the Auto-Circ scheme assumes there's only one loop in the recirculation system, which won't be the case in my setup; so the water could be the desired temperature in one loop but not in another. Three, some types of pumps last longer if they're not cycled on and off and if they run at low volumes. Four, there's some noise associated with cycling on and off. Five, you don't have to worry about your check valves failing (which they do — been there, done that) if the pump is always running.

Again, it looks like you are building piece by piece, and at greater expense, everything that a thermostatically controlled pump does for about $120.

I'm not sure why it would be greater expense. The standard system has a boiler and a pump with a thermostat. My idea would have a thermostat and a valve. I'd be using the existing water heater instead of a boiler and the existing recirculation pump.

Plus, I should get much better control of the floor temperature by placing the sensing element of the thermostat control at the floor rather than at the water pump. At least, that's my thinking.

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