20x20x2 Air Filter: Actual Size, MERV Guide & Replacement
Nominal vs actual size
| Nominal (order this) | 20 x 20 x 2 in |
|---|---|
| Actual | 19.5 x 19.5 x 1.75 in |
A 2-inch-deep version of the common square 20x20 size, used in furnace and air-handler racks and return grilles built for a thicker filter. Filterbuy's 20x20x2 product page lists the actual size as 19.5 x 19.5 x 1.75 and offers it in MERV 8, 11 and 13. Because it's square, orientation in the slot doesn't matter for fit, but the airflow arrow still does. Depth is the number to watch: a 20x20x1 (about 0.75 inch deep) leaves a gap in a 2-inch rack, and a 20x20x4 won't fit at all. 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 20x20x2:
FAQs
What is the actual size of a 20x20x2 air filter?
20x20x2 is the nominal (ordering) size. Filterbuy lists its 20x20x2 at an actual 19.5 x 19.5 x 1.75 inches (19 1/2 x 19 1/2 x 1 3/4). Other brands can differ by a fraction of an inch, so check the small print on your old frame if you're switching brands.
My old filter says 19 1/2 x 19 1/2 x 1 3/4. Is that a 20x20x2?
Yes. Round each measurement up to the nearest whole inch: 19 1/2 becomes 20 and 1 3/4 becomes 2, which gives the nominal size 20x20x2.
Can I use a 20x20x1 in a 20x20x2 slot?
Not well. A 20x20x1 is only about 0.75 inch deep, so in a 2-inch rack it leaves a gap that lets air bypass the filter. Depth must match the slot, and stacking two 1-inch filters isn't a substitute for one 2-inch filter.
Is a 20x20x2 better than a 20x20x1?
Only if your system has a 2-inch slot. A 2-inch filter has more media depth (about 1.75 inches versus 0.75), so it holds more dust between changes, but you have to use the depth your filter rack or grille was built for.
How often should I replace a 20x20x2 filter?
ENERGY STAR says to check your filter monthly and change it when it is dirty, at least every three months. Filterbuy generally recommends every 90 days, every 2 months with pets, and every 6 weeks if someone in the home has asthma or allergies.
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 — 20x20x2 air filters (actual size, replacement guidance)
- 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