On 11/15/2015 4:44 PM, Chicago Bob wrote:
I don't need a complex programmable thermostat. All I want is to know how
many hours that fan has run so I know when to change the air filter. The
fan runs frequently in the summer and winter, but very infrequently in
the spring and fall. How often the fan runs is determined by temperature.
You can go weeks - or months - without the fan running at all.

How many "fan hours" do you consider significant? For an arbitrary
(and possibly seasonally variable) figure, you could buy an elapsed
time meter and wire it in parallel with your fan motor. Or,
you can buy a cheap clock (with date indication) and use that
(i.e., change it when N days have elapsed since the date displayed
on the previous change -- I suspect if you're off by a few fan-hours
it's not going to matter to you!)