How often should I change my AC filter?
Every 30 to 60 days for a standard 1-inch pleated filter in Casselberry, and closer to 30 if you have pets or a pool cage full of pollen. A 4- or 5-inch media filter lasts 6 to 12 months. Our nine-month cooling season means these intervals are shorter here than the packet says.
How often, by filter type
| Filter | Interval here | Notes |
|---|---|---|
| 1-inch pleated, MERV 8–11 | 30–60 days | The common case. Check it monthly; the sight of it decides, not the calendar. |
| 1-inch fibreglass | 30 days | Protects the equipment, barely filters the air. |
| 4–5 inch media cabinet | 6–12 months | Far more surface area, so far less pressure drop. Usually the better answer in a restricted duct system. |
| Washable / electrostatic | Monthly rinse | Must be bone dry before it goes back in. A damp filter in a humid air stream is a mould problem. |
Shorten every interval if there are pets, if anyone in the house has allergies, during renovation work, or during Central Florida’s spring pollen weeks.
Why the expensive filter can make things worse
The counterintuitive part: a higher MERV rating is not automatically better. A denser filter adds resistance, and resistance is exactly what a 1970s Casselberry duct system does not have to spare. 57.1% of this city was built between 1970 and 1989, frequently with a single undersized central return. Fit a MERV 13 filter to a system already running near its maximum external static pressure and you reduce airflow, which reduces capacity, reduces dehumidification, and in the worst case freezes the evaporator coil.
If you want better filtration in an older house, the right answer is usually more filter area rather than a denser filter — a 4- or 5-inch media cabinet, or a second return. That is a duct decision, not a shopping decision. Test before you upgrade.
What a blocked filter does
What a neglected filter actually costs you, in order of how quickly it arrives: reduced airflow within weeks; a frozen evaporator coil in a humid month (what that looks like); a dirty evaporator coil that eventually needs cleaning or replacement at $700–$2,500+; and, over years, a shortened compressor life because the system is running with insufficient suction gas return.
It is the cheapest maintenance there is and the one most often skipped, largely because the filter in a 1970s Florida house is often in a ceiling return grille that is awkward to reach. Put a reminder in your phone for the first of the month.
Not sure what size or type yours takes?
Photograph the filter's printed size and the air handler's model number. That is enough to say whether a media cabinet would suit your system.
Phone: (689) 308-3675 · Monday-Friday, 8:00 AM - 5:00 PM
Where the facts on this page come from
Every figure above is either a primary-source document or a named third-party cost guide. All of it was checked in September 2026. Fee schedules, rebate amounts and market prices change without notice — if you are about to spend money on one of these numbers, open the source and check it.