Every time a doorway opens in an Indian commercial building, two things leave the room: conditioned air and money. A well-specified air curtain door system stops both. It creates a high-velocity, laminar sheet of air across the opening that separates inside from outside without any physical barrier. Staff, trolleys and customers walk straight through. Heat, dust, exhaust fumes and flying insects largely do not.
Air curtains have been standard in European and Middle Eastern retail for decades. In India they are still often treated as an optional extra, which is why so many installed units underperform. The technology works; the specification usually does not. What follows is a practical checklist for anyone about to buy.
How an air curtain actually works
The unit mounts above the door and discharges air downward through a narrow nozzle. The jet travels the full height of the opening, hits the floor, and splits, with part of it returning inward and part spilling outward. That returning stream is what does the sealing work. An air curtain does not simply blow air at a doorway; it builds a pressure-balanced barrier that resists the natural exchange of indoor and outdoor air.
Three numbers determine whether that barrier holds: discharge velocity at the nozzle, velocity at floor level, and the uniformity of the jet across the door width. A unit producing 12 m/s at the nozzle and 2 m/s at the floor will seal a 2.1 m doorway. The same unit on a 3 m doorway will not. The jet breaks up before it reaches the floor and you get a draught instead of a seal.
Sizing: match the unit to the opening, not the room
The single most common specification error in India is buying by room area. Air curtains are sized to the opening, not the space behind it.
Length must cover the full door width. A 900 mm unit over a 1,200 mm door leaves 300 mm unprotected, and air will preferentially rush through that gap. The seal fails at its weakest point, not on average. For wider entrances, units are installed end to end in a continuous run with no gap between housings.
Height drives the velocity requirement. As a working rule for commercial installations: openings up to 2.4 m need a standard-duty unit; 2.4 to 3.5 m need a heavy-duty or industrial model; anything above 3.5 m, such as a warehouse shutter or loading bay, needs an industrial unit with a deep nozzle and correspondingly higher throw. Suppliers who publish throw height against measured floor velocity are the ones worth shortlisting. Facilities comparing specifications usually start with a manufacturer's own range of air curtain door models, where mounting height, throw and airflow are stated per size rather than left to a single generic brochure figure.
Ambient, heated or unheated?
India's climate means most installations are unheated. The job is to keep conditioned air in and hot, dusty, humid outside air out, and an ambient unit does exactly that.
Heated versions, whether electric or hot-water coil, make sense in a narrow set of cases: cold-chain facilities where staff pass repeatedly between a chilled area and ambient conditions, hill-station hospitality, and northern industrial units where January mornings genuinely drop. Fitting a heated unit to a Mumbai retail entrance adds capital cost, a much larger electrical load and a heating element that will effectively never be switched on.
Insects, dust and the hygiene case
The airflow barrier that blocks heat also blocks airborne particulates and flying insects. This matters commercially, not just for comfort. Food processing units, pharmaceutical facilities, commercial kitchens, hospitals and packaging halls are all audited on contamination control, and an entrance air curtain is one of the cheapest measures that shows up favourably in an FSSAI or GMP inspection.
Air curtains work best as one layer of a system rather than a lone fix. A typical hygienic entrance specification pairs an air curtain at the main door with PVC strip curtains on internal transfer openings and loading bays, where traffic is slower and a physical barrier is acceptable, and an insect light trap sited away from the entrance to catch whatever does get inside. Each element handles a different failure mode. Buying only one and expecting it to do all three jobs is why some facilities wrongly conclude that air curtains do not work.
Installation and control details that decide performance
Good hardware, badly installed, performs worse than modest hardware installed correctly.
Mounting position. As close to the top of the opening as practical, and on the inside face. Mounted too high, the jet loses velocity before it reaches the floor. Mounted on the outside, wind pressure disrupts it.
Discharge angle. Most units allow a small outward tilt, typically 10 to 20 degrees. On entrances with notable outdoor wind pressure, that tilt is what keeps the jet from being pushed inward.
Door interlock. A door-mounted sensor or limit switch, so the unit runs only when the door is open, is the highest-return option on this list. Continuously running air curtains are the main reason operators complain about running cost, and about fan noise in retail interiors.
Two-speed operation. Low speed for normal hours and high speed for peak traffic or windy conditions, rather than one setting left permanently at maximum.
Serviceability. Filters and fan chambers need periodic cleaning, and in Indian urban conditions that means more often than the manual suggests. A unit with a hinged front panel gets cleaned. One that has to be dismounted does not.
What to ask a supplier before you commit
Ask for measured air velocity at floor level for your exact opening height, not just nozzle velocity. Ask for the motor make and the IP rating on industrial units. Ask whether spares such as motors, capacitors and bearings are stocked domestically, because an imported unit with a six-week lead time on a fan motor is a liability in a food or pharma facility. Ask for reference installations in your sector and, where possible, visit one and stand in the doorway. Thirty seconds under a correctly specified air curtain tells you more than any datasheet.
Finally, get the whole entrance assessed rather than a single product quoted. Door width and height, traffic frequency, internal pressure, prevailing wind direction and the equipment already installed all change the answer. Manufacturers who begin with a site assessment rather than a model number tend to specify units that still perform three years later, and if you would like your own entrances reviewed on that basis you can contact the Aircon Engineers team for a specification and quotation.