DIYrr

HVAC Air Filter: Size, MERV & How Often to Change It

Updated 2026-10-20 · Sources verified 2026-07-20

Have this exact problem? Snap a photo or describe it and get a free step-by-step plan — local prices and the permit answer included, and you can email the plan to yourself. No signup. Get my free plan →

Short answer: no permit needed. Exempt finish work under FBC 105.2 and Orange County's published list — but exempt work must still comply with the Florida Building Code. The full rule and its official source are below, with the code requirements and mistakes that trip up Orlando homeowners.

The permit answer

No permit needed. Exempt finish work under FBC 105.2 and Orange County's published list — but exempt work must still comply with the Florida Building Code.
Source: https://codes.iccsafe.org/s/FLBC2023P1/chapter-1-scope-and-administration/FLBC2023P1-Ch01-SubCh02-Sec105.2

Orange County and the City of Orlando run separate permit offices with separate portals — and your mailing address alone doesn't tell you which one covers your home. Check which permit office covers your address →

Key facts before you start

Check it monthly, change it on schedule: EPA says manufacturers 'typically recommend replacement every 60 to 90 days, but if filters appear heavily soiled when you replace them, you should consider changing them more frequently', and its own tip is to check every month, 'especially during heavy use months (winter and summer)'. In Orlando the AC runs most of the year, so monthly is the honest check.
Why it matters: a dirty or clogged filter 'can dramatically reduce air flow, increasing furnace run time, wear on the motor and energy consumption' (DOE HVAC guide). Low airflow is also how an evaporator coil freezes; if the air is weak and the line is iced, start with the filter (see the AC not cooling guide).
Which rating: EPA recommends 'a filter with at least a Minimum Efficiency Reporting Value (MERV) 13 rating, or as high a rating as your system fan and filter slot can accommodate', and says most furnaces and HVAC systems 'can accommodate a MERV 13 filter without creating equipment problems, provided that the filter is replaced frequently'.
The catch: 'Higher MERV filters do tend to restrict airflow'. DOE's guide notes the fixes are more surface area: a deeper pleated filter or 'two furnace filters side by side' in the return. With a thin 1-inch slot on an older system, a MERV 13 that is left in too long can starve the blower; if the system struggles after an upgrade, drop back or ask an HVAC tech to check static pressure.
Arrow direction: EPA's filter guidance is to 'align the arrows on the filter with the direction of the air flow through the fan', and the direction is 'marked on the side of the filter'. At a return grille that means the arrow points into the duct, toward the blower; at the air handler it points toward the blower, never out toward the room.
No gaps: EPA — make sure 'there are no gaps so air flows through the filter, not around it'. Use the exact nominal size printed on the old filter's frame; a filter that rattles in the slot is letting dust past it to the coil.

Get a free step-by-step plan for YOUR exact repair →

DIYrr builds a personalized plan from a photo and description — tools, materials with local prices, and permit guidance. Email it to yourself to keep it. Free for homeowners, no account needed.

Frequently asked questions

Do I need a permit for a HVAC air filter repair in Orange County, FL?

No permit needed. Exempt finish work under FBC 105.2 and Orange County's published list — but exempt work must still comply with the Florida Building Code.

When should I call a licensed professional instead of DIYing a HVAC air filter repair?

Check it monthly, change it on schedule: EPA says manufacturers 'typically recommend replacement every 60 to 90 days, but if filters appear heavily soiled when you replace them, you should consider changing them more frequently', and its own tip is to check every month, 'especially during heavy use months (winter and summer)'.

Related repairs

Sources

https://www.epa.gov/indoor-air-quality-iaq/what-merv-rating
https://www.epa.gov/indoor-air-quality-iaq/guide-air-cleaners-home
https://blog.epa.gov/2014/04/27/earth-mont-tip-change-your-hvac-system-filter/
https://www.energy.gov/sites/default/files/2013/11/f5/hvac_guide.pdf
https://www.epa.gov/emergencies-iaq/diy-air-cleaners
https://www.epa.gov/system/files/documents/2023-08/DIY_Air_Cleaner_Infographic.pdf

This guide is general informational content, not professional or legal advice. Codes and county rules change — confirm permit requirements with your local building department, and use a licensed professional for electrical, gas, structural, or main-line plumbing work.

Built by Karhan Construction & Remodeling, an owner-led repair and remodeling company in Orlando — DIYrr is free whether or not you ever hire us.