Hi Cathy
 CH>         Those ventilators one sees on roof tops - are they just working 
on
 CH> the air coming up?  I always thought they used electricity.
The ones I have looked at, are powered by the [horizontal] wind outside,
spinning the rotor. On the inside is a fan which then sucks the hot air out
[vertically]. Not so effective on a calm day.
If they are
 CH> then it might be possible (if they are not powered by electricity) to 
take
 CH> some power off of the moving shaft.
Have never seen electrical ones. The moving shaft might only deliver one
mouse- power!!
My roof has, I think, not very good
 CH> ventilation.  There are these funny holes in the overhang.  I do not get
 CH> very much shade either.  Ever seen anything like this?     Cathy
In OZ the funny holes on the underside of the eaves, are to provide roof 
pace
ventilation. That brings cooler air in to displace the roasting hot air in 
he
roof space. The interstices between the roof tiles are so numerous, that the
displaced air then wafts out between the tiles. In this countyr tiles are the
most common roofing. But the experience of bushfires has killed the 
opularity
of the "funny holes" as these have resulted in roof burning out of sight and
out of reach of fire hoses. These aren't included in modern homes. Ceiling
exhaust [elec] fans are popular here, in bathroom kitchen and laundry. In our
last home I added resistor/ thermostats so these fans "crawled" on freezing
days or spun fastest on hottest days.  Cheers.....ALEC
... ....The wheel is environmentally unviable
--- PPoint 1.92
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