14x24x1 Air Filter: Actual Size, MERV Guide & Replacement
Nominal vs actual size
| Nominal (order this) | 14 x 24 x 1 in |
|---|---|
| Actual | 13.38 x 23.38 x 0.75 in |
A mid-sized 1-inch filter, common in return grilles cut to a 14 by 24 opening and in some furnace and air-handler slots. Filterbuy's 14x24x1 product page lists the actual size as 13 3/8 x 23 3/8 x 3/4, while its general size chart rounds it to 13.5 x 23.5 x 0.75. Brands differ: Filterbuy's own brand comparison lists Filtrete at 13.68 x 23.68 x 0.81 and washable Air-Care at 13 5/8 x 23 5/8. Measure your old frame or slot before ordering, and don't confuse it with 14x25x1 (about 13.5 x 24.5 at Filterbuy), which is one inch longer. Filters are deliberately cut smaller than their nominal label so they slide into the slot; length and width typically run about 1/4 to 1/2 inch under nominal. Actual sizes vary slightly by brand, so compare against the small print on your old frame.
How to measure
- Turn the system off at the thermostat (and the service switch) before pulling the filter.
- Read the frame first: the large print is the nominal size (what you order); small print, if present, is the actual size.
- If there is no label, measure length, width and depth edge to edge with a tape measure.
- Round each measurement up to the nearest whole inch to get the nominal size (e.g. 19.5 x 24.5 x 0.75 → 20x25x1).
- No old filter? Measure the filter slot or cabinet opening the same way.
- Note the airflow arrow: it should point toward the furnace or blower.
MERV 8 vs 11 vs 13
| MERV | Minimum capture (EPA / ASHRAE 52.2) | Good for |
|---|---|---|
| 8 | ≥20% of 1–3 µm, ≥70% of 3–10 µm | Basic dust, pollen, lint; the minimum EPA Indoor airPLUS requires |
| 11 | ≥20% of 0.3–1 µm, ≥65% of 1–3 µm, ≥85% of 3–10 µm | A step up for pets and allergies |
| 13 | ≥50% of 0.3–1 µm, ≥85% of 1–3 µm, ≥90% of 3–10 µm | EPA's recommended level for fine particles (PM2.5), if your system can accommodate it |
EPA notes that higher-MERV filters tend to restrict airflow, and recommends using the highest rating your system fan and filter slot can accommodate. Most systems handle MERV 13 if the filter is replaced frequently. Thin 1-inch slots are the most restrictive; deeper 4-inch media filters generally create less static pressure. Weak airflow from vents, a system that runs longer, or a filter that bows are signs to step down a grade or ask an HVAC technician.
How often to replace
ENERGY STAR: check your filter every month and change it when it looks dirty, at least every three months. Pets, dust, renovations and heavy heating/cooling seasons can mean more frequent changes.
Equivalent & nearby sizes
There is no exact substitute for a different size: length, width and depth must all match. These nearby sizes are commonly confused with 14x24x1:
FAQs
What is the actual size of a 14x24x1 air filter?
14x24x1 is the nominal (ordering) size. Filterbuy's 14x24x1 product page lists the actual size as 13.38 x 23.38 x 0.75 inches (13 3/8 x 23 3/8 x 3/4); its general size chart rounds this to 13.5 x 23.5 x 0.75. Other brands differ slightly (Filterbuy lists Filtrete at 13.68 x 23.68 x 0.81), so check the actual dimensions printed on your old frame if you're switching brands.
My old filter says 13 3/8 x 23 3/8 x 3/4. Is that a 14x24x1?
Yes. Round each measurement up to the nearest whole inch: 13 3/8 becomes 14, 23 3/8 becomes 24 and 3/4 becomes 1, which gives the nominal size 14x24x1.
Can I use a 14x25x1 instead?
No. A 14x25x1 is about an inch longer and won't seat properly in a 14x24 slot. Length, width and depth must all match so air doesn't bypass the filter.
Can I cut down a larger filter to fit?
No. Cutting a filter breaks its frame and seal, and length, width and depth must all match the slot so air doesn't bypass the filter. Buy the 14x24x1 size.
How often should I replace a 14x24x1 filter?
ENERGY STAR says to check your filter monthly and change it when it is dirty, at least every three months. Homes with pets, dust or construction may need more frequent changes.
Is MERV 13 safe for my system?
EPA says most furnaces and HVAC systems can accommodate a MERV 13 filter without equipment problems if it is replaced frequently, but higher-MERV filters do tend to restrict airflow. If you notice weak airflow or are unsure, ask an HVAC technician.
Which way does the arrow go?
Per ENERGY STAR, the airflow arrow on the filter frame should point toward the furnace or blower unit.
Sources
- Filterbuy — 14x24x1 air filters (actual size, actual cut by brand)
- Filterbuy — Air filter sizes chart (nominal vs actual)
- Aerostar — Air filter sizes: nominal vs actual
- US EPA — What is a MERV rating?
- US EPA — Guide to Air Cleaners in the Home
- US EPA Indoor airPLUS — Filtration technical bulletin
- ENERGY STAR — How to keep your HVAC system working efficiently
- ENERGY STAR — Certified Homes maintenance guide