By the way looking at it really doesn't tell you the condition if you have
an electrostatic filter. According to Filtrete the electronstatic fibers
loose their ability to atttrack the smallest particles before the filter is
otherwise dirty.


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?

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).