Weather Louvres

Frequently asked questions

What is a weather louvre?

A weather louvre is a frame fitted with angled blades that covers an external opening in a wall, plant enclosure or ventilation intake. The blade angle turns away rain and wind-driven water while air still passes through the gaps. Most also carry a bird mesh on the back. Use a weather louvre on every external ventilation opening, and an internal grille or diffuser inside the building.

Weather louvre or grille: which do I need?

A grille has straight or adjustable blades that direct or screen air but give no weather protection, so it belongs inside the building on supply, return and transfer openings. A weather louvre is built for the outside face of the building. If you need control over the airflow as well as weather protection, fit a volume control damper directly behind the louvre.

What free area does a weather louvre give?

Free area is the open part of the louvre face that air can actually pass through. On our standard blade profiles it rises with size, reaching around 45 to 49% on large louvres, but on small sizes the frame takes a bigger share and a 300 x 300 louvre gives roughly 22 to 31%. That is why a louvre always needs to be larger than the duct it serves. Insect mesh reduces free area further. Send us the airflow you need to pass and we will size the louvre on the free area, not the overall face size.

What size weather louvre do I need?

Size the louvre on airflow and face velocity, not on the duct diameter. Work out the free area needed to pass your airflow at a sensible velocity through the blades, then choose a louvre whose free area meets it. Undersized louvres cause noise, high pressure drop on the fan and rain being drawn through the blades. For a standard opening up to 600mm square, the stock range covers it. For anything larger or non-standard, we size and draw it for you.

Stock or made to order?

Our stock aluminium square louvres from 150mm to 600mm and the circular louvres suit standard openings and ship next working day. Choose made to order when the opening is a non-standard size, when the louvre must match the building in a RAL colour, when you need stainless steel for a coastal or chemical environment, or when the opening is too large for a single unit. Made to order louvres come with a drawing for approval and have a ten working day lead time from approval.

Can I get weather louvres in a custom colour or stainless steel?

Yes, on made to order louvres. Satin anodised aluminium is the standard finish, and any RAL or BS colour is available powder coated. Marine grade 316 stainless steel suits coastal and chemically aggressive sites. Stock louvres are supplied in mill finish aluminium.

How quickly can I get a bespoke louvre?

Ten working days from drawing approval. We confirm sizes and finish, issue a drawing showing every dimension and flange detail, and production starts once you approve it. If you have a hard project deadline, tell us at the start and we will confirm what is achievable before you commit.

Can you make very large louvres?

Yes. Openings larger than a single unit are supplied as sectional louvres with jointing details and intermediate mullions shown on the drawing, so they assemble on site into one continuous louvre face. Send us the overall opening size and we will design the split.

Do you supply louvres for trade and commercial projects?

Yes. We supply M&E contractors, cladding and roofing contractors, facilities teams and housing providers, with trade pricing and no minimum order. Send a schedule or drawing and we will quote stock and made to order louvres together. Call 0161 399 3825 or email hello@efans.co.uk.