wrote in message
oups.com...
When a home air filter manufacturer recommends a filter change every
90 days, what duty cycle do they assume the filter wil be used?
1 hour per day?
10 hours per day?
24 hours per day?

You need to change it every 90 days, unless it needs to be changed sooner,
or operating conditions result in you being able to change it less
frequently.

I think they should list filter change recommendations in hours (e.g.
filter good for 300 hours of use).
(Some thermostats like my LUX have filter-life counters that show the
number of hours the filter was used since it was last changed).

You should be able to call LUX and ask them how many hours you can go
between filter changes. After all, they put the hour meter in there, so they
should be able to tell you how to use it. But then, they don't make filters,
so their guess is as good as..... If they give any answer, and don't just
hang up on you. At least one of the manuals they have online gives their
theory as to how many hours = 90 days, and it's not any of the guesses that
you've made. So, my first answer is likely to be the most correct answer.

If you don't like these answers, you'll need a new thermostat.