An air curtain is a focused stream of air blown across a doorway or opening to form an invisible barrier that separates two spaces without a physical door. By maintaining a high-velocity sheet of air (typically 6 to 12 m/s at the discharge), it stops draughts, dust, insects, and conditioned-air loss while letting people and vehicles pass freely. Air curtains are fitted above entrances of shops, cold stores, cleanrooms, and loading docks, cutting energy loss through open doors by 30% to 80% compared with an unprotected opening.
How an Air Curtain Works
A fan draws room or outdoor air, accelerates it through a narrow nozzle, and projects a uniform laminar sheet down across the opening. The jet's momentum holds back the cross-flow of outside air, temperature gradients, and contaminants. Effective coverage needs the curtain to span the full width and reach the floor or the opposite header; for a 2.4 m high door the discharge velocity should stay above 6 m/s at the threshold to remain intact against ambient draughts.
Main Types of Air Curtains
Non-recirculating (ambient) units blow unheated air and suit interior shop doors. Heated air curtains add electric or hot-water coils (3 to 30 kW) for cold-climate entrances, warming the airstream to 30–45°C. Industrial/cold-store curtains are high-velocity and often heated to protect freezers at −18°C to −25°C. Revolving-door and telescopic types serve special openings. Widths cover 0.6 to 2.0 m per module, joined for wider doors.
Installation and Sizing Numbers
Match the unit length to the door width (within ±50 mm) and the nozzle velocity to the height: doors up to 2.5 m need 6–8 m/s, taller industrial doors up to 4 m need 9–12 m/s. Mount the unit plumb and as close to the header as possible, with the discharge angled 10° to 15° outward to deflect incoming air. Electric heated models draw 3 to 30 kW, so size the supply and confirm the control interlocks with the door.
Air Curtain Type Comparison
| Type | Discharge velocity | Heating | Best use |
|---|---|---|---|
| Ambient | 6–9 m/s | None | Interior / mild climate |
| Heated electric | 7–11 m/s | 3–30 kW | Cold entrances |
| Cold-store | 9–12 m/s | Hot-water / electric | Freezers −25°C |
| Industrial | 8–12 m/s | Optional | Loading docks |
Selection Checklist
- Choose an ambient air curtain for interior doors in climate-controlled buildings.
- Choose a heated curtain when the entrance faces winter below 5°C outside.
- Size velocity to door height: 6–8 m/s up to 2.5 m, 9–12 m/s above that.
- Match unit width to the opening within ±50 mm and mount at the header.
- Interlock the heater with the door and fan so it runs only when needed.
Common Installation Errors
The most frequent mistake is mounting the unit too far below the header, which lets the air sheet detach before reaching the floor and lets draughts through. Keep the nozzle within 50 to 100 mm of the opening top and plumb to the door. A second error is wrong velocity: below 6 m/s the curtain breaks in any breeze, while above 12 m/s it blows papers and feels harsh. A third is leaving gaps at the sides, so size the module to the full width and join units seamlessly for doors wider than 2 m to keep the barrier continuous and effective.
Maintenance
Clean the inlet grille and nozzle every 3 to 6 months; a 1 mm dust film on the nozzle can cut discharge velocity by 10% to 15% and let outside air in. Check the fan balance annually, because imbalance raises vibration and noise above the rated 50 to 60 dB(A). For heated models, test the coil or elements each season and confirm the interlock closes the heater when the door is shut, avoiding wasted 3 to 30 kW of heat and a fire risk from a blocked airstream that cannot carry the energy safely away outside.
Measuring Effectiveness
Verify performance with an anemometer at the threshold: the centre-line velocity should still exceed 4 m/s at floor level for a 2.5 m door, proving the sheet reaches intact. A thermal imaging check can show where conditioned air escapes around the curtain. If the reading is low, raise the fan speed within its rated range or reseal the mounting; if it is fine, you can typically trim 5% to 10% of speed in mild weather to save energy while still holding the barrier against light draughts and insects entering the space.
Specifying for Cold Stores
Freezer doors at −18°C to −25°C need a high-velocity, often heated curtain to stop fog and ice at the threshold and to protect the room from warm, moist outside air that would raise coil load by 20% to 40%. Use a vinyl-ester or stainless airstream rated for the duty, with the discharge aimed slightly outward to throw warm air away from the cold floor. Pair it with a rapid-action door so total open time stays under a few minutes per hour, keeping the energy penalty small and manageable for the plant.
Summary for Specifiers
An air curtain pays back by stopping the open-door energy leak, typically saving 30% to 80% of the HVAC loss at that opening. Size velocity to door height, mount at the header, and interlock the heater with the door. Whether ambient or heated, a correctly aimed sheet keeps comfort, insects, and dust out while letting traffic flow, making it one of the simplest, fastest-return efficiency measures in any busy entrance or loading area of a building.
Quick Reference Numbers
Key air-curtain figures: 6 to 12 m/s discharge, 0.6 to 2.0 m width per module, 3 to 30 kW heat, and 30% to 80% HVAC loss saved at the opening. Doors up to 2.5 m need 6 to 8 m/s, taller ones 9 to 12 m/s, with the nozzle 50 to 100 mm from the header. Freezer duty protects rooms at −25°C. Anchoring the layout to these ranges ensures the sheet stays intact against draughts and the unit earns its payback within one to two heating seasons in cold climates without complaint from occupants.
Keruite manufactures this equipment at an 80,000 m² facility in Dezhou, China, with an in-house AMCA-210-style test laboratory; every unit is balanced to G2.5 and performance-tested before shipment.
FAQ
Does an air curtain really save energy?
Yes. By sealing the doorway with a moving air sheet, a correctly specified air curtain reduces conditioned-air loss through open doors by 30% to 80% compared with an unprotected opening, lowering heating and cooling load. The fan uses only a fraction of the energy the lost HVAC air would cost, so payback is often under two heating seasons in cold climates.
What velocity does an air curtain need?
Discharge velocity should be 6 to 8 m/s for doors up to 2.5 m high and 9 to 12 m/s for taller industrial openings up to 4 m, measured at the nozzle. Too low and ambient draughts break the sheet; too high and the curtain itself becomes uncomfortable and noisy. Match the velocity to the door height rather than using a single fixed setting.
Should I heat the air curtain?
Heat the curtain only at cold-climate entrances where the stream must also warm people and offset the incoming cold, typically with 3 to 30 kW. For interior doors, mild climates, or cold-store thresholds, an unheated ambient curtain is enough and saves the heater's electrical load while still blocking draughts and contaminants.
Can an air curtain keep out insects and dust?
A continuous, well-aimed air sheet at 6 m/s or above discourages flying insects and blocks most airborne dust and odours from crossing the threshold, which is why air curtains are common at food plants and cleanrooms. Effectiveness depends on full-width coverage and correct angle; gaps or misalignment let pests and particles through.