Air Prefilters: G1–G4 Guide to Extending HEPA & ULPA Filter Life
What Is an Air Prefilter?
A prefilter is a coarse or medium-efficiency air filter placed upstream of a HEPA or ULPA filter. Its job is to catch large particles — dust, fibres, pollen and airborne debris — before they reach the expensive final filter. By doing so, a prefilter dramatically extends the service life of your HEPA/ULPA filters and reduces total filtration cost.
Onecleans manufactures prefilters in-house across the G1–G4 efficiency range, including panel and pleated designs for cleanrooms, AHUs and industrial processes.
Prefilter Efficiency Grades: G1 to G4
Prefilters are classified under EN 779 / ISO 16890 by their coarse and fine particle efficiency:
| Grade | Arrestance / Efficiency | Typical Use |
|---|---|---|
| G1 | Coarse (low) | Basic dust protection for HVAC |
| G2 | Coarse–medium | General ventilation, first-stage protection |
| G3 | Medium | Pre-filter for comfort air and light industrial |
| G4 | Fine (90%+ arrestance) | Standard prefilter before HEPA/ULPA |
The G4 Panel Prefilter is our most popular choice for protecting HEPA and ULPA filters in cleanrooms and HVAC systems.
Why Prefilters Matter
- Longer final-filter life — a good prefilter can double or triple HEPA/ULPA service life.
- Lower operating cost — prefilters are cheap; final filters are not.
- Stable airflow — protecting the HEPA/ULPA keeps pressure drop from climbing prematurely.
- Energy savings — cleaner final filters run at lower resistance, cutting fan energy.
Types of Prefilters
Panel Prefilters
Flat or pleated panels in cardboard or metal frames, used as the first stage in AHUs and air intakes. Low cost and easy to replace.
Pleated Prefilters
Pleated media in a rigid frame provides more surface area and lower resistance than flat panels, ideal for high-airflow or dusty environments.
High-Temperature Prefilters
For hot processes such as spray painting and coating lines, we supply 300°C high-temperature pleat prefilters that protect downstream high-temperature HEPA filters.
How to Choose a Prefilter
- Match efficiency to the load — G4 is standard before HEPA/ULPA; lower grades suit comfort HVAC.
- Check temperature — high-heat processes need high-temperature prefilters.
- Size to the housing — panel or pleated, in standard or custom dimensions.
- Plan replacement intervals — prefilters are replaced more often than final filters.
Related Reading
- HEPA Filters: The Complete Guide
- High Temperature HEPA Filters: The Complete Guide
- How Often Should You Replace HEPA Filters?
Frequently Asked Questions
What is the difference between G4 and F-class filters?
G4 is a coarse/fine prefilter (EN 779); F-class (F7–F9) are fine filters that sit between a G4 prefilter and a HEPA/ULPA in demanding systems.
How often should prefilters be replaced?
Typically every 1–6 months depending on ambient dust load. Monitor pressure drop and replace when it reaches the recommended limit.
Can prefilters be washed?
Some coarse prefilters are washable, but pleated and high-temperature prefilters are usually disposable. We can advise based on your application.
Request a prefilter quote — specify your grade, size and temperature for factory-direct pricing.