On Tue, 29 Aug 2006 22:18:31 GMT, CJT wrote:

mm wrote:

On Sun, 27 Aug 2006 18:24:58 GMT, CJT wrote:


I have a gable mounted, thermostatically controlled attic exhaust
fan which I use to hold down attic temps. I know some people think
those are not energy efficient, but I've made my decision and it is
not the subject here.

It occurs to me that there are times when the fan is running needlessly,
because even though the attic is hot enough to trigger the thermostat,
the attic temp and outside temp are almost the same, so the fan is
simply replacing hot air with air that is almost as hot.


When is it you think this is true? I have an attic fan in the roof
and I can't think of any time when it is hot enough to turn the fan on
that it it isn't quite a bit hotter inside the roof than outside.

For instance, on very hot nights the attic temp can eventually
approximate the outdoor temp while both are still quite hot.

I"ve found that the fan turns off between 7PM and 10PM, rarely going
as late as 10, depending on how sunny and hot the day had been.

The fact that it turns off implies to me that for some time before
then, it was cooling off with cooler outside air.

And my experience when I walk outside after sundown is that it cools
off more quickly than even does the second floor of my house. (I
rarely use AC)

I have doubts that it is ever as hot outside as it is inside the attic
after sundown.

If I ever again see an indoor/outdoor thermometer at a yard sale,
maybe I'll get it, so I can know "for sure".