What Filtration Efficiency do I Need for my Facility?
What Filtration Efficiency do I Need for my Facility?
There are many factors that determine what air filtration efficiency is best for your application. Things to consider include particle size, density, CFM (cubic feet per minute) required, whether venting inside or out, and cost. Filtration efficiency can be confusing because different testing methods, particle sizes, and industry terminology are often used to describe filter performance. This article explains the most common terms and compares the efficiency of several industrial filtration methods.
Particle Size
To understand filtration efficiency, you first need to understand particle size. MERV ratings evaluate filters using three particle size ranges:
- 3–10 microns
- 1–3 microns
- 0.3–1 micron
(ULPA filters are tested down to 0.12 microns.)
For comparison, a human hair is approximately 70 microns in diameter, while a red blood cell measures about 8 microns in diameter. Thermally generated oil smoke typically ranges from 0.1 to 1 micron, making it one of the more challenging contaminants to capture efficiently.
This diagram shows the size range of common airborne particulates.
MERV Ratings
One of the most common ways to compare filter efficiency is the MERV (Minimum Efficiency Reporting Value) rating. MERV ratings measure how efficiently a filter captures different particle sizes. The higher the MERV rating, the greater the filtration efficiency.
| Rating | 0.3–1 Micron | 1–3 Micron | 3–10 Micron |
| MERV 1–4 | — | — | <20% |
| MERV 5 | — | — | ≥20% |
| MERV 6 | — | — | ≥35% |
| MERV 7 | — | — | ≥50% |
| MERV 8 | — | ≥20% | ≥70% |
| MERV 9 | — | ≥35% | ≥75% |
| MERV 10 | — | ≥50% | ≥80% |
| MERV 11 | ≥20% | ≥65% | ≥85% |
| MERV 12 | ≥35% | ≥80% | ≥90% |
| MERV 13 | ≥50% | ≥85% | ≥90% |
| MERV 14 | ≥75% | ≥90% | ≥95% |
| MERV 15 | ≥85% | ≥90% | ≥95% |
| MERV 16 | ≥95% | ≥95% | ≥95% |
| HEPA (MERV 17–19) | ≥99.97% | ≥99.97% | ≥99.97% |
| ULPA (MERV 20) | ≥99.9995% | ≥99.9995% | ≥99.9995% |
Sometimes filter efficiency is listed only as a percentage rather than a MERV rating. This can be misleading because the percentage depends on the particle size being tested. For example, a 95% efficient filter could be rated anywhere from MERV 14 to MERV 16, depending on which particle size it captures at that efficiency. When comparing filters, always ask for the MERV rating, not just the efficiency percentage.
HEPA and ULPA Filters
Filters rated above MERV 16 are generally classified as HEPA or ULPA filters rather than by their MERV rating. HEPA filters are commonly used in industrial manufacturing, laboratories, healthcare facilities, and clean rooms because they remove at least 99.97% of 0.3-micron particles. ULPA filters are even more efficient but are typically reserved for extremely critical environments where the highest possible level of cleanliness is required.
Some DOP panel filters are marketed as HEPA-style filters because they are interchangeable with HEPA filters. However, they are not necessarily 99.97% efficient. These filters often have a longer service life than true HEPA filters and may provide a more economical option when maximum filtration efficiency is not required.
Many industrial mist collectors use HEPA filters as the final stage of filtration, including Absolent®, Donaldson Torit, 3nine, and other multi-stage filtration systems. While the final HEPA filter is highly efficient, its service life depends heavily on the performance of the prefilters. If the earlier filtration stages allow excessive particulate to reach the HEPA filter, replacement costs can increase significantly.
Electrostatic Filtration Efficiency
Electrostatic filtration is another highly effective method for collecting wet particulate, especially oil smoke generated by CNC machining and other manufacturing processes.
When properly maintained, a single stage of electrostatic filtration is typically 90%–95% efficient on 0.3–1 micron particles, depending on airflow and equipment design. Adding a second electrostatic stage can increase efficiency to 99% or greater. Some manufacturers incorporate third or fourth collection stages to increase airflow capacity while also providing redundancy if one stage temporarily loses efficiency.
SmogHog, MistBuster, Tri-Mist, Trion, and Aerocology are among the best-known electrostatic air cleaner brands used throughout North American manufacturing facilities.
Capture Efficiency
One of the most overlooked aspects of any air filtration system is capture efficiency.
Capture efficiency measures how much airborne particulate is actually captured by the system before it escapes into the workplace. Poor hood design, undersized ductwork, inadequate airflow, plugged filters, or improperly designed source capture can dramatically reduce overall system performance.
For example, if 15% of the smoke escapes before it ever reaches the filtration system, the difference between a 95% efficient filter and a 99.97% efficient filter becomes much less significant. Improving source capture often has a greater impact on workplace air quality than simply upgrading to a higher-efficiency filter.
Designing the system to capture contaminants at their source is the most important step in creating an effective industrial air filtration solution.
Need Help Choosing the Right Filtration System?
Whether you are evaluating electrostatic air cleaners, HEPA filtration systems, or other industrial mist and smoke collection equipment, Bee Clean Specialties can help you compare filtration efficiency, maintenance costs, and long-term operating expenses. Give us a call at 888-451-0844 to discuss the best filtration solution for your facility.