dogsnus looks for:

reliability and _quietness_...

Lasko's 2155A 2470 90 W window fan is nice--$53 from Ace Hardware. For
summer use, in an upstairs window behind some homemade poly film louvers
hinged at the top that only allow exhaust airflow, with more louvers
inside a downstairs window that only allow intake airflow. Turn off the AC
(if any) and turn on the the fan when outdoor air is cooler using a
Goldline differential thermostat from Grainger in series with a room
temp thermostat to turn it off when the room air becomes too cool.

And maybe cool a basement with lots of thermal mass below the comfort temp
at night and turn on another fan during the day to circulate air between
the basement and living space as needed to keep it cool with no ventilation
to the outdoors.

For winter use, reverse the louvers and fan and add humidity controls to
turn off the furnace and turn on the fan to warm and dehumidify the house
and avoid condensation on a warm day.

Some day soon, we may see a computer that does all this with an adaptive
algorithm and wireless Sensiron RH/temp sensors and X10/Insteon controls.

Nick