Most HVAC filters list a nominal size (like 18x20x1) that’s rounded for easy shopping. The actual size is often slightly smaller so it fits into the slot or grille. For example, many 18x20x1 filters measure about 17.5" x 19.5" x 0.75".

• Check your current filter: Measure length, width, and thickness and note both nominal and actual sizes printed on the frame.
• Review product details: Product pages list the actual size—match that to your opening if tolerances are tight.
• Aim for a snug fit: Avoid gaps that let air bypass the filter. Don’t force a too-large filter.

You can compare actual sizes online and choose pickup or delivery for convenience.

The main difference is thickness and the amount of filter media. An 18x20x2 filter typically has more pleats than a 1-inch version, which can help with airflow and service life at a similar MERV rating, though results vary by system.

• Compatibility: Only use a 2-inch filter if your furnace/return grille is designed for it.
• Performance: More media can reduce pressure drop compared to thinner filters of equal rating, but this depends on the product and your HVAC.
• Do not stack: Avoid stacking two 1-inch filters to mimic a 2-inch filter.

Check your unit’s manual and the filter slot depth before choosing; then select the thickness that fits your setup.

MERV indicates how well a filter captures particles. Choosing a rating is about balancing filtration and airflow that your system can handle.

• MERV 5–8: Basic dust and lint—good for general protection.
• MERV 9–11: Better capture of pollen and pet dander for many homes.
• MERV 12–13: Finer particles, including smoke and smaller aerosols.

Higher MERV filters can be more restrictive, which may affect some HVAC systems. It’s a good idea to check your equipment manual or consult a technician before moving up in rating. Also, some packages use alternative rating scales—look for the listed MERV equivalent on the packaging to compare apples to apples.

Reusable filters are designed to be washed and reinstalled, following the manufacturer’s directions.

1. Turn off your system and remove the filter.
2. Rinse both sides with gentle water flow; use mild soap only if the maker allows.
3. Air-dry completely before reinstalling. Some models note machine-wash or dryer-safe on the label—follow only what your specific filter states.
4. Reinstall with the airflow arrow pointing the right direction.

Tip: Inspect monthly and clean when visibly dirty. Many reusable options are rated around MERV 8, while higher-MERV disposable filters are also available if you need finer filtration. Choose the approach that fits your air quality goals and HVAC recommendations.

Use the arrow printed on the filter’s frame as your guide—it shows the direction of airflow.

• At a return grille: Arrow should point into the duct or wall.
• At the furnace/air handler: Arrow should point toward the equipment (toward the blower).
• Fit matters: Ensure the filter sits snugly with no gaps along the edges.
• Close panels securely: Replace the grille or furnace door before turning the system back on.

Mark the install date on the frame to help track changes. If your setup is unusual, checking your HVAC manual can help confirm orientation for your specific system.