On Mon, 16 Nov 2015 04:45:02 -0800 (PST), trader_4
wrote:

I see your point, but the OP isn't the only one that thinks
fan run time is relevant. I've seen thermostats from major
manufacturers that have a filter indicator that goes on
based on hours of fan run time. I've never bothered with it
though. Like you, I just check and/or change based on length
of use and past experience.

Why does evenything have to be high-tech?

Most people just change their filters when they look dirty, or change
them 2 or more times a year, based on the calendar or when the heating &
cooling seasons begin.