Nominal vs. Actual Air Filter Sizes Explained

When replacing air filters in your property’s HVAC system, you’ve likely encountered the terms "nominal size" and "actual size." Understanding these terms is essential for ensuring a proper fit and maintaining optimal performance. This guide explains the differences between nominal and actual air filter sizes, how to measure your filter correctly, and why getting the right size matters for property managers.

What Are Nominal and Actual Air Filter Sizes?

Nominal Size

The nominal size is the rounded measurement of an air filter’s dimensions. Manufacturers use this standard labeling system to simplify purchasing, but it doesn’t reflect the filter’s precise dimensions.

For example, a filter labeled 20x25x1 has a nominal size of 20 inches wide, 25 inches tall, and 1 inch thick. These numbers are rounded to the nearest whole inch for convenience.

Actual Size

The actual size represents the filter’s exact dimensions, typically slightly smaller than the nominal size to ensure the filter fits snugly into the designated slot. A filter with a nominal size of 20x25x1 may have an actual size of 19.5x24.5x0.75 inches.

Why the Difference?

The discrepancy allows the filter to fit within the frame or housing without being too tight, which could hinder airflow or damage the filter.

How to Measure Your Air Filter

If you’re unsure of your air filter’s size, follow these steps to measure it accurately:

1. Remove the Old Filter

Carefully slide the old filter out of the HVAC system. Take note of its orientation to ensure proper installation of the new filter.

2. Measure the Dimensions

Use a tape measure to determine the exact width, height, and depth of the filter.

• Width: Measure the shorter side.
• Height: Measure the longer side.
• Depth: Measure the thickness of the filter.

3. Check the Label

Most filters have the nominal size printed on the side. If the label is missing, use your measurements as a reference to find the actual size and match it to the nearest nominal size.

Accurate measurements are crucial for selecting the right filter size and ensuring your HVAC system operates efficiently.

Why Choosing the Correct Filter Size Matters

1. Improved Air Quality

An ill-fitting filter can allow unfiltered air to bypass the system, reducing its effectiveness at capturing dust, pollen, and other contaminants.

2. Optimal HVAC Performance

A filter that’s too small may leave gaps, while one that’s too large can bend or damage the housing. Both scenarios can strain your HVAC system and reduce its efficiency.

3. Reduced Energy Costs

Properly sized filters help maintain consistent airflow, which prevents the system from overworking and keeps energy costs in check.

4. Extended Equipment Lifespan

Filters that fit correctly protect the HVAC system from dirt and debris, reducing wear and tear on components.

Common Mistakes When Buying Air Filters

1. Assuming All Filters Are the Same

Not all filters labeled with the same nominal size have identical actual sizes. Different brands may vary slightly, so always check the actual size.

2. Ignoring Filter Thickness

While the width and height are often prioritized, the thickness is just as important. A filter that’s too thick can restrict airflow.

3. Relying Solely on the Old Filter’s Size

If the previous filter was incorrectly sized, using it as a reference can perpetuate the problem. Measure the actual dimensions of the filter housing for accuracy.

How to Find the Right Replacement Filter

1. Check the Manufacturer’s Recommendations

Consult your HVAC system’s manual or contact the manufacturer for the recommended filter size and type.

2. Use Online Tools

Many manufacturers offer online sizing tools to match your system with the appropriate filter.

3. Work with a Trusted Supplier

Purchase filters from reputable suppliers to ensure quality and compatibility with your HVAC system.

FAQs About Air Filter Sizes

Q: What if I can’t find the exact size filter for my HVAC system?

A: If the exact size isn’t available, choose a filter that’s slightly smaller rather than one that’s too large. Use foam tape or a gasket to fill any gaps and ensure a secure fit.

Q: Can I use a thicker filter for better performance?

A: Thicker filters may offer better filtration but can restrict airflow if your HVAC system isn’t designed for them. Always follow the manufacturer’s specifications.

Q: How often should I replace air filters?

A: Replace filters every 1-3 months, depending on usage, filter type, and environmental factors such as pet dander or construction dust.

Beagle’s Support for Property Managers

Managing HVAC systems across multiple properties can be a logistical challenge for property managers. Beagle’s Your Renters Kit includes tools designed to simplify maintenance and improve tenant satisfaction:

• Air Filter Delivery Service: Ensures tenants receive the correct filters on time, reducing system strain and extending HVAC lifespan.
• Maintenance Reminders: Automates notifications for filter replacements, helping tenants stay on top of their responsibilities.

These features are included at no cost to property managers, making Beagle an essential partner for streamlined operations.

Final Thoughts

Understanding the difference between nominal and actual air filter sizes is essential for maintaining your HVAC system’s efficiency and air quality. By choosing the correct filter size and following best practices, property managers can reduce maintenance costs, enhance tenant satisfaction, and extend the life of their HVAC systems. With Beagle’s free tools and services, staying on top of air filter management has never been easier.

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Related Blog Posts:

• MERV Ratings Explained | Choosing the Right Air Filter for Your Property
• What MERV Rating Should Property Managers Use? | Optimize Air Quality & HVAC Efficiency
• Air Filter Delivery Services | How Small Conveniences Improve Tenant Satisfaction

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