With the 4" media filters, you can typically let them go a year. They actually filter better as they get loaded. If your system is a reasonably new Carrier system, it probably has an ECM motor, which are programmed to deliver a specific number of cubic feet per minute regardless of the static pressure (up to a point). In other words, as the filter gets loaded the fan maintains the same airflow through your ducts. You can visually check the filter and replace when it looks "really loaded". I suspect the tendency is to change the 4" filters before they really need to be changed, particularly if you have previously had a system with 1" filters.
Quote:
Originally Posted by bagboy
My unit requires a Merv8 filter measuring 19x20x4.5. I used to buy them at Ace Hardware but there was a little play in them when installed. My HVAC people said that is not a good thing. They recommended Home Depot for the Merv8. I tried theirs and they fit perfectly. They are less than $30, but could last up to one year. I replace them every 6 to 8 months.
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