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Door width X meters, door height Y meters – what size and air speed air curtain do you need?
This is one of the most common questions we hear from purchasing agents, distributors and contractors.The core function of an air curtain is to create an invisible air barrier that separates indoor and outdoor air. But if the size or air speed is wrong, the barrier will have gaps – and the effectiveness drops significantly, or even fails completely.Follow these three steps to select the right model quickly.Step 1: Determine the length – door width decides the air curtain sizeThe length of the air curtain must cover the entire door width – preferably slightly longer.If the air curtain is shorter than the door, gaps will form on both sides, allowing cold and warm air to exchange. Data shows that insufficient width can lead to a noticeable increase in air exchange.Length selection principle:Air curtain length ≥ Door widthFor doors wider than a single units standard length (e.g., a 4-meter-wide entrance), multiple units can be installed side by side. For example, a 4-meter-wide door can be covered by 3 air curtains installed in parallel.Step 2: Determine the type and air speed – door height decides the fan type and speed requirementDoor height is another critical factor in air curtain selection. The higher the door, the farther the airflow needs to reach – and the higher the air speed required.Door height under 3 meters:This is the most common application scenario for air curtains. Most standard models can handle it.Recommended fan type: Cross-flow air curtainRecommended nozzle air speed: 8–12 m/sRequired floor-level terminal air speed: 6–8 m/sTypical applications: Retail stores, restaurants, offices, convenience storesDoor height 3–4 meters:When door height exceeds 3 meters, standard cross-flow air curtains struggle to deliver effective airflow to the floor. A more powerful model is needed.Recommended fan type: Centrifugal air curtainRecommended nozzle air speed: 13–18 m/sRequired floor-level terminal air speed: ≥9 m/sTypical applications: Warehouses, workshops, supermarket entrancesDoor height above 4 meters:Extra-high doorways require special treatment. Standard models are generally not sufficient.Recommended solution: Custom extra-long air curtains or high-static-pressure modelsRecommended nozzle air speed: 18–25 m/sAlternative approach: Multi-unit staged installation at different heights to create an airflow relayTypical applications: Industrial plants, logistics warehouses, large cold storage facilitiesStep 3: Verify that the air speed is sufficientAir speed is the core indicator of whether an air curtain will work effectively. Pay attention to two key data points during selection:1. Nozzle air speed (rated speed): The speed value listed in the product specifications. However, this value decreases as installation height increases.2. Floor-level terminal air speed (actual performance): The remaining air speed when the airflow reaches the floor. This is the critical metric that determines real-world effectiveness.Reference on decay: The higher the installation height, the more the air speed decays. Each increase in mounting height results in a corresponding loss of terminal air speed at floor level.Quick Selection ReferenceDoor height under 3m: Cross-flow type, 8–12 m/s nozzle speed, ≥6 m/s at floor levelDoor height 3–4m: Centrifugal type, 13–18 m/s nozzle speed, ≥9 m/s at floor levelDoor height above 4m: Custom / high-static type, 18–25 m/s nozzle speed, ≥12 m/s at floor levelLength principle: Air curtain length must cover the full door width. For wide doors, multiple units can be installed side by side.Want to verify the numbers for your project?We've built a free online tool – the Air Velocity Calculator. Enter your airflow and duct size, and get instant results. No registration required.👉 Try it here: www.miwindair.com/air-velocity-calculatorNeed a more precise selection recommendation?If you already have specific door dimensions and installation conditions, feel free to contact us directly. We can provide more accurate model recommendations and technical specifications based on your actual parameters.DM or WhatsApp: +86 133 9275 3256Website: www.miwindair.com