Air Filter Size Chart 2025: Find Your Exact Size by Brand & Model Number

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💡 Tip: Find the size/model on your current filter's frame or in your HVAC manual

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🔍 Quick Tip: Finding Your Filter Size

Check the side of your current filter for the printed size, or measure Length x Width x Depth and round up to the nearest inch. Always order by nominal size unless the manufacturer specifies otherwise.

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⚠️ Important: Why Actual Size Matters for Whole-House Filters

Notice how the same nominal size (like 16x25x5) has different actual dimensions across brands? This is why you should always search by model number or actual size when ordering whole-house filters. Standard 1-inch filters are more universal, but thicker filters require exact brand compatibility.

🫁 When MERV 13 Makes a Real Difference

While MERV 11 works well for most homes, MERV 13 provides hospital-grade filtration for specific health situations:

Most families with mild seasonal allergies do well with MERV 11 - save MERV 13 for serious respiratory concerns.

Air Flow Rule: The arrow on your filter should point TOWARD the furnace/air handler and AWAY from the return duct. Air flows from the room → into the filter (front) → out toward the equipment (back).

What's the difference between nominal and actual filter size?

Nominal size is the rounded size printed on the filter label (like 20x20x1), while actual size is the exact measurement (like 19.5x19.5x0.75). Always order by the nominal size unless specifically instructed otherwise.

Can I use a different brand filter if the nominal size matches?

For standard 1-inch, 2-inch, and 4-inch filters: Yes! These sizes are standardized across brands. A 20x20x1 from any manufacturer will fit a 20x20x1 slot.

For whole-house filters (typically 3-6 inches thick): Be careful - nominal sizes DON'T guarantee compatibility. Actual dimensions vary significantly by brand and model number.

Example: Not All 16x25x5 Filters Are The Same

A Honeywell FC100A1029 has the nominal size 16x25x5, but the actual measurements are 15¾" x 24¾" x 4⅜".

A Lennox X6670 also has the nominal size 16x25x5, but the actual measurements are 15¾" x 24¾" x 4⅜" - which happens to match!

However, a Carrier FILXXCAR0016 (also labeled 16x25x5) has different actual dimensions and won't fit the same slot.

How to Find the Right Whole-House Filter:

1. Search by model number (e.g., "FC100A1029") - most reliable method
2. Search by actual size (e.g., "15¾ x 24¾ x 4⅜") if you can measure your current filter
3. Check compatibility - our product pages list which brand models each filter fits

Need help? Call us at 910-401-3910 with your filter's model number or measurements, and we'll find your exact match!

What if my filter size is too big or too small?

Too big: Won't fit properly and may damage when forcing it in, creating gaps for unfiltered air.
Too small: Leaves gaps around edges, allowing dust and allergens into your HVAC system, reducing efficiency and indoor air quality.

How do I find my filter size without an old filter?

1. Look for a size printed on the filter slot or door
2. Measure the filter opening and round up to the nearest inch
3. Check your HVAC system manual or model number online
4. Contact us at 910-401-3910 with your HVAC model - we'll help find the right size

How often should I change my furnace filter?

1-inch filters: Every 30-90 days depending on usage, pets, and allergies
2-inch filters: Every 2-3 months
4-inch+ filters: Every 3-6 months

Check monthly and replace when visibly dirty or when airflow seems restricted.

Why Choose Atomic Filters vs FilterKing & FilterBuy?

Can't Find Your Size?

We carry over 400+ sizes including custom dimensions. If your size isn't listed:

• 📞 Call us at 910-401-3910
• 💬 Use our live chat (bottom right)
• 📧 Email: info@atomicfilters.com

We'll find your exact size or create a custom filter!

View Complete Detailed Size Chart with All MERV Options →

Ready to Find Your Perfect Filter?

Browse our complete selection of air filters in all sizes and MERV ratings

Questions? Call us at 910-401-3910 or email info@atomicfilters.com