How to Read a Particulate Efficiency Graph on an Air Filter Report

When two air filters carry similar class labels, the particle efficiency graph can reveal important differences in how they perform across particle sizes. That matters for engineers, contractors and buyers who need more than a broad rating to make a sound selection.

An efficiency curve helps you see where a filter is strong, where performance starts to fall away, and how it may behave in the real system. If you know what to look for, the graph becomes one of the most useful parts of a filter report.

What a particulate efficiency graph shows

A particulate efficiency graph plots filter efficiency against particle size. In most reports, particle size appears along the horizontal axis, usually in microns, while efficiency appears on the vertical axis as a percentage.

The curve shows how well the filter captures particles at each size point tested. A higher point on the graph means more particles are being captured at that size. A lower point means more particles are passing through.

In practical terms, the graph helps answer questions such as:

• •Does the filter perform evenly across a wide range of particle sizes?
• •Is there a dip in performance near the most penetrating particle size?
• •Does the filter become more effective on larger particles, smaller particles, or both?
• •Is the curve shaped in a way that suits the application and dust load?

This is useful because class labels can group filters broadly, but two filters with the same class can still behave differently across the particle range.

Why the curve matters when class labels look similar

Class labels are a starting point, not the full story. MERV, EN 779 and ISO 16890 classifications do not convert directly, so comparing a label from one standard to another can be misleading if you stop there.

Even within the same standard, the efficiency curve can show meaningful differences. Two filters may sit in the same class, yet one may hold performance more consistently across the sizes that matter for your site.

That is why the graph is worth checking when you are deciding between options such as:

• •two filters with the same class but different construction
• •a standard filter versus a deeper pleated option
• •a lower-resistance filter versus a higher-efficiency model
• •a filter being considered for a sensitive process or a dustier environment

If the application is tied to ventilation design, AS 1668.2:2024 should be considered alongside site requirements, and those requirements should be confirmed with the mechanical services engineer or building owner.

How to read the axes and curve shape

Start with the particle size scale

Look for the units on the horizontal axis. Some reports show a range of particle sizes in microns, while others may use test points specific to the standard.

Smaller particles generally sit towards one end of the graph, with larger particles at the other. The exact layout depends on the report format, so always read the axis labels carefully before comparing curves.

Check the efficiency line, not just the peak

A curve that rises steeply may indicate the filter becomes much more effective as particle size increases. A flatter curve may indicate more even performance across the range.

Do not focus only on the highest point. A useful graph is one that shows how the filter behaves across the whole particle size range relevant to your system.

Look for the most penetrating particle size

The most penetrating particle size, or MPPS, is the particle size at which the filter is least efficient. This is a key point in the curve because it identifies the area where the filter has the hardest time capturing particles.

For HEPA filters, EN 1822 class ratings are defined at the MPPS. Under that standard:

• •H13 is at least 99.95% efficient at MPPS
• •H14 is at least 99.995% efficient at MPPS

If you are comparing HEPA options, the MPPS performance is more important than a broad statement about total efficiency alone.

How to use the graph in a buying decision

A particulate efficiency graph is most useful when you match it to the job, not just the label.

Consider the operating environment first. A cleaner indoor space, a general HVAC system and a dustier industrial site will place different demands on the filter. The right curve for one setting may not be the best choice for another.

Then compare these points:

• •the particle sizes you care about most
• •whether the curve is stable or sharply uneven
• •the filter’s resistance, if the report includes pressure drop data
• •whether the filter format suits the existing frame or housing
• •how the filter may affect servicing access and maintenance planning

If you need help measuring an existing filter, our guide on how to measure an air filter is a practical place to start before ordering a replacement.

When two filters look close on paper

Sometimes the curves are nearly identical and the decision comes down to build, fit and handling. In that case, check the full product details, including media type, frame material, depth and sealing method.

If the housing or system is non-standard, a custom air filters option may be the more practical path than forcing a near-match into place.

What else to check on the report

An efficiency graph should not be read in isolation. A sensible selection also considers the rest of the report and the system it is going into.

Look for:

• •initial pressure drop, if provided
• •test standard used
• •airflow conditions at which the data was taken
• •whether the report shows average efficiency or size-specific efficiency
• •any notes about installation orientation or sealing requirements

A filter with strong efficiency on paper may still be a poor fit if it creates an unsuitable pressure drop for the system or does not suit the frame. The report should support the mechanical design, not override it.

Some filters are designed to be washable - check the product instructions before cleaning or reusing any filter. Washability is a product-specific feature, not a general rule.

Common mistakes when comparing efficiency curves

Treating all standards as interchangeable

Do not assume MERV, EN 779 and ISO 16890 mean the same thing. They are different rating systems and do not convert directly. Use the actual report for the filter you are considering.

Reading one point instead of the whole curve

A single efficiency number can hide a dip at a critical size. The curve gives a fuller picture of how the filter behaves across the range.

Ignoring the application

A filter chosen for a comfort cooling system may not be the best choice for a process area, plant room or dusty intake. The right graph is the one that matches the site conditions and the intended use.

Forgetting about maintenance planning

Inspection frequency depends on the system, site conditions and dust load. Follow the filter and equipment manufacturer instructions, and monitor pressure drop where gauges are fitted.

If ongoing servicing is needed, our filter servicing and commercial filter servicing information can help you plan the next step.

Getting the right filter for the job

A particulate efficiency graph is one of the best tools for comparing filters with similar class labels because it shows how the filter performs at different particle sizes, not just how it is classified. For engineers and buyers, that means a better basis for selecting a filter that fits the system, the application and the maintenance approach.

Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, established 2009. We can supply or make the right filters for your setup, including standard and custom air filters, and support a range of industries we supply.

To discuss a filter report, compare options or request a quote, call 07 3800 3448 or contact us.