External Louvres
External weather louvres finish the outside end of a ductwork system, letting air in or out while keeping rain and debris off the duct. Ours are made from durable, lightweight aluminium in a classic angled-blade design that balances weather protection with airflow, and the range covers circular, square and made-to-measure rectangular formats.
Which weather louvre do I need?
For round ducting terminating through a wall, a circular weather louvre in 100mm to 315mm diameters connects directly to the duct. Square louvres run from 150mm x 150mm up to 1000mm x 1000mm neck size and suit square openings or connection to round duct via a plenum box. Where the opening is rectangular — plant-room intakes, facade vents, builder’s-work openings — our custom rectangular weather louvre is made to your exact size, anywhere from 150mm up to 1800mm wide and 2400mm high, with an instant price calculated online as you type the dimensions. No waiting for a quote.
On all our louvres the size you order is the neck size, with the overall face 50mm larger on both axes; each product page spells out both dimensions. If you need something outside the listed ranges, we can make other sizes to order — just ask.
Stock and delivery
Stocked circular and square sizes ordered by 3pm go out for next-day delivery; made-to-measure rectangular louvres show their lead time on the product page. We are a Leicester-based UK supplier, and UK mainland delivery is free on orders over £400 ex VAT.
External Louvres for Ventilation Systems
External louvres are mounted on the outside face of a building wherever a ventilation duct terminates at an external wall. They serve as the weather barrier, preventing rain, wind-driven water, snow, leaves, birds, and debris from entering the ductwork while permitting the required volume of air to pass through for supply or exhaust ventilation.
Blade Design and Rain Defence
Our louvres feature profiled aluminium blades set at an angle (typically 45°) that deflects falling rain outward while channelling water to drainage gutters at the blade edges. The blade pitch and profile are engineered to reject rain at wind speeds up to 13 m/s (force 6) without significant water penetration. For sites exposed to severe weather, we offer enhanced-defence louvre profiles with deeper blades and additional drainage channels.
Free Area and Airflow
The free area of a louvre is the effective open area available for airflow, expressed as a percentage of the overall face dimensions. Our standard louvres offer approximately 45–50% free area. When sizing a louvre, calculate the required free area from your airflow rate and target face velocity (typically 2.0–2.5 m/s for intake louvres), then select a louvre whose free area meets or exceeds that figure.
Materials and Finishes
- Mill-finish aluminium — our standard finish, lightweight and corrosion-resistant, suitable for most installations
- Powder coating — any RAL Classic colour for an architectural finish that matches the building facade. Popular choices include RAL 9010 (Pure White), RAL 7016 (Anthracite Grey), and RAL 9005 (Jet Black)
- Anodised aluminium — available to order for a durable, low-maintenance satin finish
Insect Screens and Bird Guards
We offer optional insect mesh (typically 6 mm aluminium woven mesh) fitted behind the louvre blades to prevent insects and small birds entering the ductwork. For areas with pigeon or seagull problems, heavier bird-guard mesh can be specified. Note that mesh reduces the effective free area, so allow for this in your sizing calculations.
Bespoke Manufacturing
Alpha Air manufactures external louvres in-house at our Leicester facility. While we hold a range of standard sizes in stock, we routinely produce bespoke louvres to exact project dimensions, typically within 3–5 working days. Architectural louvres with special profiles, extended frames, or flanged returns are also available.
Why Choose Alpha Air?
With many years of louvre manufacturing experience, we combine quality craftsmanship with fast turnaround. Standard sizes dispatch same day. Bespoke louvres are manufactured to your specification within days, not weeks. Free delivery on orders over £400. Call 0116 246 0031 for sizing calculations, RAL colour matching, or project pricing.
Frequently Asked Questions
How do I calculate the louvre size I need?
Divide your required airflow rate (in m3/s) by the target face velocity (typically 2.0-2.5 m/s for intake louvres) to get the required free area in m2. Then divide by the louvre’s free area percentage (e.g. 0.45 for 45%) to get the total face area needed. Our team can do this calculation for you on 0116 246 0031.
Can I get a louvre in a specific RAL colour?
Yes. We offer powder coating to any RAL Classic colour code. Provide your RAL number when ordering and we will coat the louvre to match. Powder-coated louvres typically add 1-2 working days to the lead time compared to mill-finish.
Do external louvres come with insect mesh?
Insect mesh is available as an option on all our external louvres. Specify mesh when ordering and we will fit it during manufacture. Remember that mesh reduces the effective free area by approximately 15-20%, so upsize the louvre accordingly.
What is the lead time for bespoke-size louvres?
Bespoke louvres are typically manufactured within 3 to 5 working days from order confirmation. For large quantities or special profiles, lead times may be slightly longer. Contact us for a specific lead time based on your project requirements.