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Subject:  Re: Radiant Heat System Date:  1/9/2004  8:21 AM
Author:  Goofyhoofy Number:  44410 of 137203

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).

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.

One, I guess that's true but I'm not sure it's important. Again, if you have "enough", you merely adjust the cycle time at the pump to reflect how much radiation you want from the pipes. This is the same as adjusting the thermostat on the first floor to tell the boiler in the basement how often to charge the radiator, isn't it?

Two, not exactly true. And you are confusing the Auto-Circ, which is meant for "undersink" with the 909 (and similar from other manufacturers) which is meant to drive a standard recirculation system, usually near the HWH, not the sink. They are different systems, designed for different applications. I didn't investigate, but I know they have systems which run different "zones" off the same pump.

Three, probably true. However I've been running the undersink auto-circ for several years, 24/7, pulsing as it wants to, without trouble of any kind. It's still as quiet and functional as the day I got it.

Four, there is no noise associated with either the Auto-Circ or the 909. None. Nada. They are maddeningly silent. It is impossible to tell if they are running, or when they switch on and off. Indeed, to get the timing breaks, I had hook up a (homemade) seismometer device on a flexible line to detect the pump switch on and off. In fact, sometimes I can't tell, even by holding the pump in my hand, whether the pump is running, the vibration is so slight, and it is impossible to tell by listening, even lying with your head under the sink next to the pump (been there), when they switch on or off.

Five, I don't know about check valves. I've never had one fail. Certainly possible.

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.

Well here we disagree. I don't get a variation of more than 2/10 of a degree over time in any given place; it takes so long for the heat to transfer through the subfloor, concrete board, tiles that any "pulsing" from the system is completely camouflaged. I found the temperature I want, it stays there and doesn't move. (I've noted that I have some variances by location (+/- 3 degrees), one of which I can explain as being at the junction of the subfloor plywood, two others I have no explanation for at all.)

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