How to know when to change
I can see you are trying hard to analyze this problem, and taking lots of measurements and providing lots of facts. However it seems to me you still are not talking the language that the pros speak, sorry to say.
It is my understanding that a filter needs to be changed when its pressure drop exceeds a certain amount due to loading up, no sooner and no later. All the things people say, be it 3 weeks or once a year, are at best attempts to estimate this pressure drop without knowing any measurements. At worst they are marketing mis-truths designed to sell a product (usually their filter).
If there is any way to measure the ESP ("External Static Pressure") of your system, that would give you numbers you could use to answer your question. Many AC techs have the tools to measure this, I suspect they could be used more often to good advantage. If your tech would measure ESP before and after your filter change, that would give you some useful info.
The proper way to measure is a manometer or gauge with one tube leading to before the filter (i.e. in the house air) and the other tube leading to after. I have done this with a Dwyer red-oil manometer bought on Ebay -- but I am a nut about this stuff and don't expect you to do the same. Dwyer professionally documents this application for commercial installations, where there is more money at stake.
There is also a little "G-99" gauge intended to measure pressure drop changes across the filter, specifically intended to tell you when filter change is needed.
It is cheap and simple, and looked good to me -- but somebody on the board told me they disapproved of it, I forgot what they said but it sounded like a professional opinion at the time. Still, how could this be a waste of $15?
Hope this helps -- P.Student
Filter It Requirement is HIGHLY SUBJECTive
Originally posted by wendel
Filter was a MERV 8 pleated filter.
.. life of a filter on a properly designed system would be--
A more messy household would shorten this value. A retired couple could lengthen it.
NICE calc absolutely requires validation and modification:
Is 83 hours or changing a MERV 7 ( or 8 ) filter ~ every 10 days realistic?
What FILTER dP and AIR FLOW did you measure
with Clean Filter? Dirty?
Use Merv 7 ... Measure and Track over an extended period.
Seems like you would have to decrease air flow > 20% to make significant, noticeable difference in A/C performance.
Actually, retired couple may be MORE SENSITIVE & at HOME 3 times more than others, so MORE frequent filter change may be required.