Before you call
Which Air Filter to Buy for the System You Have
Buy the size printed on the filter in the system. MERV 8 is the everyday choice. A higher rating can choke an older blower.
The size is printed on the frame of the filter that is in the slot. Buy that size. A filter that has to be forced in is the wrong filter, and it will bend and bypass.
MERV, without the brochure
MERV 8 is the everyday pleated filter for most residential systems. It catches dust without pretending to be a hospital filter. MERV 11 is reasonable if the blower was sized for it.
MERV 13 in a system that was not designed for it raises static pressure. The signs are a loud return, a coil that ices, and a blower that runs hot. If someone in the house needs heavier filtration, a separate air cleaner is the honest answer, not a thicker filter in a one-inch slot.
How often
One to three months. Pets, smoke, and construction dust are the short end. Write the date on the frame. A filter on a subscription is fine. A filter you never see is how independent AC repair becomes a July emergency.
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