Carrier Filter Replacement — Sizes, MERV Ratings, and Schedule

Finding your filter size

Carrier residential air handlers use a filter cabinet attached to the return side. Common sizes: 16x25x1, 20x25x1, 16x25x4, 20x25x4. Look at your current filter — the size is printed on the cardboard frame. The 4-inch (media) filters last longer and resist airflow better than 1-inch.

MERV rating — what to use

• MERV 8 — basic dust and pollen, lowest airflow resistance
• MERV 11 — pet dander, mold spores (our default for Treasure Coast homes)
• MERV 13 — fine particles, allergens (great if you have allergies, watch for static pressure)
• Higher than MERV 13 — only on systems specifically designed for it (Carrier Infinity Air Purifier handles up to MERV 15)

How often to replace

• 1-inch filter: every 30–60 days in Florida — sooner with pets or remodeling
• 4-inch media filter: every 6–12 months
• Visual check monthly — when light won't pass through it, change it

What a dirty filter does

Restricts airflow, drops coil temperature below freezing, ices the evaporator coil. Iced coil melts when system shuts down, floods the pan, trips the float switch. 'No cool' service calls — many of them start with a $15 filter someone forgot to change.