Once you know the size of the opening, the next decision is not always as simple as picking a vent off the shelf. A louvre vent is a ventilation cover with angled slats that let air pass through a wall, door or duct opening while keeping rain out and stopping leaves, insects and debris from getting in. Beyond size, there are choices around shape, colour and flyscreen type that affect how well a vent fits and how it looks once fitted. This guide covers rectangular versus circular louvre vents, the narrow letterbox style, the five standard colours, and fixed versus removable flyscreens, so you can pick the right variant with confidence.
Rectangular vs Circular Louvre Vents: Which Shape Suits Your Opening
The traditional rectangular or square louvre vent, in sizes such as 9x3, 9x6 and 9x9 inch, is the standard choice for airbricks and most wall openings. A brick course opening is rectangular, so a rectangular louvre vent cover sits flush against the brickwork without gaps to fill or make good. If you are replacing an existing airbrick cover, or fitting a new one into a wall built with standard brick coursing, a rectangular vent louvre is almost always the natural fit and the one that looks correctly proportioned against the surrounding wall.
Circular louvre vents, available in this range at 165mm diameter, offer the same angled slat ventilation in a round profile, and they suit a different set of situations. Soffits are the obvious one: a round hole is far easier to core drill cleanly into a soffit board than a rectangular one is to cut neatly, so a circular vent louvre is often both quicker to fit and tidier once finished. The same logic applies to smaller openings generally, wherever drilling a round hole beats chiselling or cutting a square one. Many homeowners also prefer the look of a circular louvre grille in certain settings, since the round shape reads as more discreet and modern than a boxy rectangular cover, particularly on smooth render or painted soffit boards.
The Securit Circular Louvred Vent 165mm in black and the white version are both popular for soffit and duct applications where a neat round finish matters. Whichever shape you choose, browse the full louvre vent collection to compare every size and finish before ordering.
The Narrow Letterbox Style: A Different Shape Again
There is a third shape worth knowing about, and it solves a problem that neither the rectangular nor the circular vent can. The long, narrow letterbox style louvre vent, available at 26x2 inch in aluminium, is designed for slim openings above doors or in skirting where a standard square vent will not fit. A 9x3 inch vent is too tall for these locations, and a circular vent does not suit a slot shape at all, so the letterbox profile fills a genuine gap in what is otherwise available.
Because this style is only available in aluminium, it is a metal louvre vent by default, which means the Securit Aluminium Louvre Vent 26 x 2 Inch can be used where a gas appliance rated vent is required, something plastic cannot offer. If your opening is narrow and long rather than square or round, this is the variant to look at first, and the aluminium build holds its shape and finish over time in a slim, high traffic slot above an internal door.
Matching Vent Colour to Your Wall, Door or Trim
Shape decides what will physically fit, but colour decides how much attention the vent draws once fitted. Standard finishes across this range include white, brown, black, grey and terracotta, and matching the vent to what surrounds it makes a real difference to how noticeable it ends up looking.
White louvre vent covers are the natural choice against light brickwork, white uPVC trims, and pale painted render, since most modern extensions and outbuildings use white trim somewhere, and a white vent disappears into that scheme rather than standing out. Brown vents work the other way, blending into darker brickwork, wooden doors and fascias. If your property has traditional dark red brick, or timber finished in a mid to dark brown stain, a brown louvre vent cover sits far more comfortably than a white one would.
Black louvre vent options, available on the circular vents in this range, give a more contemporary and deliberately discreet look, popular on renovated properties with dark window frames or anthracite render, where a black vent louvre reads as an intentional design detail. Grey is the neutral option most commonly seen on ducting grilles, working well wherever surrounding pipework or trim is already grey. Terracotta suits red brick, clay roof tiles and warm toned render, matching tones that white, brown or grey cannot.
The practical rule is simple: look at the material directly around the opening, whether brick, render, a door or a fascia board, and choose the vent colour closest to it. It costs nothing extra to pick the right colour, but it is the biggest factor in whether a vent looks like it belongs. Compare the white and brown circular vents against your own wall colour before ordering if you are unsure.
Fixed vs Removable Flyscreen: Which Should You Choose
On rectangular plastic vents, there is a further choice once shape and colour are settled: fixed or removable flyscreen. A fixed flyscreen is riveted permanently into the vent body, keeping it securely in place for the life of the product, but it can only be wiped clean from the front while still fitted. This suits most standard living space locations, where dust builds up slowly and a quick wipe is all that is needed.
A removable flyscreen clips out of the frame instead, so it can be lifted out, cleaned properly, and clipped back in once dry. This is particularly useful in dustier locations such as sheds, garages and workshops, where mesh can clog far more quickly than indoors and a wipe is not enough to keep airflow clear. If sawdust, soil or general grime is a regular feature of the space, a removable flyscreen saves replacing the vent sooner than necessary.
It is worth being clear about what a flyscreen can and cannot do. Neither a fixed nor a removable flyscreen is fine enough to stop mice or other rodents, only a dedicated fine rodent mesh achieves that. If rodent access is a specific concern, the flyscreen choice on a standard louvre vent will not solve it on its own, and a rodent mesh product should be considered separately.
Both flyscreen types are available across the 9x3 and 9x6 range, including the Securit White Plastic Louvre Vent 9x3 Inch with removable flyscreen for higher dust locations, and the Securit Brown Plastic Louvre Vent 9x6 Inch with fixed flyscreen for a lower maintenance option in a larger size.
Putting It All Together
When choosing between these variants, the practical starting point is the opening itself, since its shape and size dictate what will physically fit. From there, check whether the vent needs to be gas appliance rated, meaning aluminium rather than plastic. Next comes colour, matched to the wall, door or trim around the opening. Finally, if you have settled on a rectangular plastic vent, decide between a fixed flyscreen for easy locations and a removable one for dustier settings. Working through the decision in that order takes the guesswork out of an otherwise overwhelming number of options.
Frequently Asked Questions
Can I fit a circular louvre vent into a rectangular airbrick opening?
Not cleanly. A circular vent is designed for a round hole, so fitting one into a rectangular airbrick opening leaves gaps that need making good with render or filler. For a standard airbrick, a rectangular louvre vent cover is the better match, and circular vents are best kept for soffits, ducting and other genuinely round openings.
Do all the colour finishes come in every shape and size?
No, availability varies by shape. The circular 165mm vents in this range come in black, white and brown, the rectangular plastic vents are offered in white and brown, and the aluminium options come in a metal finish rather than the five standard colours. Always check the specific product listing for the colour options available on that shape and size before ordering.
Is a black louvre vent as effective as a white one?
Yes, colour has no effect on airflow or performance. Black, white, brown, grey and terracotta louvre vents all use the same angled slat design, so the colour choice is about how the vent looks against your wall, door or trim, not how well it ventilates.
Which flyscreen type should I choose for a garden shed?
A removable flyscreen is generally the better choice for sheds, garages and workshops, since these locations tend to generate more dust and debris than a typical living space. Being able to unclip the mesh, clean it properly, and clip it back in keeps airflow clear for longer than a fixed flyscreen in the same setting.
