Recently, many customers have inquired about the differences between primary, medium, and high efficiency air filters. Today, we’ll explain this systematically. The main differences lie in: different materials and different filtration levels.
Primary Air Filters
Primary air filters are suitable for the initial filtration stage of air conditioning systems. Their filtration efficiency standards are:
- G1: 40%@5.0μm
- G2: 65%@5.0μm
- G3: 85%@5.0μm
- G4: 90%@5.0μm (measured by weight method).
They primarily filter dust particles larger than 5μm. Primary filters come in three styles: flat panel, folded, and bag-type. Frame materials include cardboard, aluminum, galvanized iron, and stainless steel (for high-temperature resistance). Filter materials include non-woven fabric, nylon mesh, activated carbon, and metal mesh. Protective screens are often double-sided plastic-coated or galvanized wire mesh.
Features: Low cost, lightweight, versatile, compact.
Applications: Pre-filtration for central air conditioning and ventilation systems, pre-filtration for large air compressors, clean air return systems, pre-filtration for local high-efficiency filtration devices. High-temperature-resistant filters (stainless steel frames) can withstand 250–300°C.
These filters are commonly used for primary filtration in HVAC systems or in simple systems requiring only one-stage filtration.
Medium Efficiency Air Filters
Medium efficiency air filters belong to the F-series in air filtration. They include bag-type (F5, F6, F7, F8, F9) and non-bag-type (FB, FS, FV). Efficiency ratings (by colorimetry):
F5: 40–50%
F6: 60–70%
F7: 75–85%
F8: 85–95%
F9: 99%.
Features:
- Captures 1–5μm particles and suspended matter.
- Heat-sealed structure reduces leakage risks.
- High airflow, low resistance, high dust-holding capacity.
- Reusable and cleanable.
- Materials: Special non-woven fabric or fiberglass.
- Efficiency: 60–95%@1–5μm (colorimetry).
- Max operating conditions: 80°C, 80% humidity.
Applications: Medium filtration in central air conditioning, pharmaceuticals, hospitals, electronics, food industries, and as pre-filters for high-efficiency systems to extend their lifespan.
High Efficiency Air Filters
Designed to capture particles smaller than 0.5μm.
Structure: Frames include aluminum alloy, multi-layer plywood, aluminum plate, or galvanized steel. Common
shapes: cuboid.
Filter material: Mostly fiberglass or PTFE (electrostatic poly tetra fluoro ethylene). Each unit is tested via the sodium flame method for high efficiency, low resistance, and high dust capacity.
Applications: Cleanrooms in industries like optics, LCD manufacturing, biopharma, precision instruments, food & beverage, and PCB production. Types include partitioned, non-partitioned, high-airflow, and ultra-high-efficiency filters.
Filtration Efficiency Summary
| Class | Removal Rating @Rated Air Flow |
Removal Rating @20% Rated Air Flow |
Initial Resistance (Pa) |
| A | >=0.5μm, >=99.9 | — | <=190 |
| B | >=0.5μm, >=99.99 | >=99.99 | <=220 |
| C | >=0.5μm, >=99.999 | >=99.99 | <=250 |
| D | >=0.1μm, >=99.999 | >=0.1μm, >=99.999 | <=280 |
