The attic is well insulated from the house, but on the hottest days upstairs is warmer than downstairs by a few degrees. To reduce the excess, an attic fan is recommended. This is simply an exhaust fan that pumps hot air out of the roof cavity through, usually, a gable vent. The fan is thermostatically controlled.
Yours truly installed the mechanism, which is remarkably easy.
Since the gables are old they were not quite the standard size,
so a small amount of cowling was required to get efficient operation.
The thermostat has been set to 95 degrees. This might seem high,
and is 5F more than typical, but the attic, we discovered, gets
very hot indeed... 90 is typical even on a day when the
oitside air temperature is a cool 70 degrees.
We have installed a switch, in the main East bedroom. This is to allow the fan to be switched off. This is typically used in case it is still operating in the evening and you want to sleep. In practice our fan is quite quiet, but in the interest of economy we usually leave it turned off... after all, no point having it on if the warmth is pleasing or you are going away and do not care too much.