Z-Line Cassette G4 Filter 550×330×48mm — primary AHU prefilter, galvanised metal frame

What a G4 filter is and where it fits

The G4 filter is the first filtration stage of any multi-stage ventilation system. Its role is to capture coarse airborne particles — dust, lint, textile fibres, small insects, large pollen — before air reaches the fine filters (F7, F9) or HEPA filters that are far more expensive.

The practical analogy: the G4 filter acts as a coarse sieve protecting the fine sieve. Without an effective G4 — or one left too long without replacement — the downstream F7 or HEPA filter clogs rapidly with coarse particles it was not designed to handle. Replacement cost of an F7 or HEPA filter is 3–10× higher than a G4 — regular G4 replacement is the cheapest investment in AHU maintenance.

Where the Z-Line Cassette G4 filter is installed:

• First stage of air handling units (AHU) — primary filtration section
• Heat recovery ventilation units — before the heat exchanger
• Centralised air conditioning systems — protecting cooling/heating coil
• Industrial ventilation systems — pre-treatment of externally drawn air

Why cassette Z-Line format over standard flat panel

Greater filtration surface area — Z-folded media increases contact surface with airflow versus a flat panel of the same frame dimensions. Greater surface area means lower initial pressure drop, higher dust holding capacity (slower loading between replacements) and more uniform efficiency across the whole surface.

Better mechanical resistance — folds provide structural rigidity to the filter media. The filter withstands pressure variations without deforming or tearing.

Better thermal resistance — cassette format with galvanised metal frame tolerates temperatures up to 80°C — superior to cardboard-framed flat panel filters (maximum 40–50°C). Relevant for installations near heat sources or industrial applications.

Full technical specifications

How to verify you have the correct size

Before ordering, measure the AHU frame with a ruler — do not rely on dimensions written on the old filter. Used filters may have deformed slightly, giving incorrect readings.

The nominal dimension 550×330×48mm is the external dimension of the metal frame. The filter must fit firmly in the AHU frame with no gaps at the edges — any lateral gap allows untreated air to bypass the filter, reducing efficiency to zero.

FAQ — EN

What is the difference between G4 and F7 or F9? G4 captures coarse particles (≥10 microns) with ≥85% efficiency — dust, lint, fibres. F7 captures fine particles (≥1 micron) with ≥85% efficiency — large bacteria, spores, fine allergens. F9 captures very fine particles with ≥95% efficiency. G4 is always first in the cascade — without it, F7 and F9 clog rapidly and maintenance costs escalate.

Can it be cleaned and reused? Z-Line cassette G4 filters are not recommended for cleaning and reuse — folds can deform during jet air or water cleaning, reducing efficiency and creating gaps for particles to pass through unretained. Periodic replacement is the correct and more economical long-term solution.

What happens if I do not replace the filter on time? A loaded G4 filter increases aeraulic resistance — the AHU works harder for the same airflow, energy consumption rises, motor service life falls. The filter may also fail mechanically under high differential pressure, allowing coarse dust through to downstream filters.

Are the 550×330×48mm dimensions external or of the opening? External dimensions of the metal frame. Verify the AHU opening matches these dimensions with a maximum 1–2mm clearance per side for correct sealing.

👉 Z-Line Cassette G4 filters — all available sizes 👉 F7 filters for second filtration stage

📞 +40 722 667 239 — free consultancy for AHU filter selection