Install Air Vent

Installing an air vent — through a brick wall, cavity wall, or rendered face — is a small but skilled job that typically costs £120–£280 for a single vent fitted in the UK. The work involves core drilling a precise hole through the wall, fitting the vent grille and any internal fan or sleeve, and weatherproofing both faces. A competent builder or core driller can complete one in 1–2 hours.

Common reasons to install a new vent: extractor fan ducting (bathroom or kitchen), cooker hood through-the-wall vent, gas appliance ventilation requirements (boilers, hobs, fires), or general background ventilation in over-tight rooms.

Typical UK costs

What core drilling actually involves

Modern vent installs use a diamond-tipped core drill rather than a hammer drill — the resulting hole is clean, round, and the right diameter first time. The drill is mounted to the wall on a bracket so it stays straight, and a water feed (or a vacuum on dry-cut systems) keeps dust and heat down.

For a 4-inch extract vent through a 9-inch (225 mm) cavity wall, the drilling itself takes 15–30 minutes. The remaining time is fitting the sleeve through the cavity, sealing the cavity (so cold air can't leak through the wall), fitting the internal and external grilles, and making good with mortar or sealant.

Choosing the right vent for the job

• Extract fan vent — paired with a 100 mm or 125 mm in-line or wall fan. Choose external grille based on bird/insect mesh and shutter type. Backdraft shutters prevent cold air ingress when fan is off.
• Cooker hood vent — typically 125 mm or 150 mm to match the hood spec. Choose a low-resistance external grille; cheap mesh grilles can cut hood efficiency by 30%+.
• Boiler / gas-appliance vent — sizing per manufacturer instructions; positioning per Gas Safe regulations (minimum distances from windows, doors, parking spaces). Get the boiler installer to specify exact location.
• Background ventilation grille — passive, no fan. Often required by Building Regs for new windows in older homes that previously relied on draughty frames.

Things people often miss

• Cavity sealing — a poorly-fitted vent that doesn't seal the cavity becomes a route for cold air, wind-driven rain, and even insects to enter the cavity. A proper sleeve through the cavity prevents this.
• External grille direction — louvred grilles must face downwards so rain runs off the slats. Fitted upside-down (a surprisingly common error) they funnel water in.
• Distance from windows — extract vents (especially kitchen and bathroom) should be at least 600 mm horizontally from any opening window or door, otherwise you re-import the air you just expelled.
• Listed buildings — exterior alterations to listed buildings need consent; even a small vent can be refused if it affects the elevation. Check with the local conservation officer first.
• Lintel positioning — drilling into or near a lintel is a structural risk. A core driller will inspect from inside before committing to a position; chasing through a lintel can mean structural repair.

Frequently asked questions

Can I install an air vent myself?

For internal-only vents (passive grille between rooms, or a fan through plasterboard), often yes. For an external vent through brick, cavity wall, or render — strongly recommend a pro with a core drill. A wrongly-placed hammer-drill hole through a cavity wall causes more damage than the £150 saved.

How long does it take to install one vent?

1–2 hours for a single 4–6 inch vent through a standard cavity wall, including making good. Multi-vent jobs are faster per vent — figure 45 minutes per additional vent.

Do I need planning permission for an external vent?

Almost never for a standard extract or boiler vent in non-listed properties — counts as permitted development. Listed buildings, conservation areas, and front-of-house elevations may need consent. Ask the local planning officer if in doubt.

What size vent do I need?

4-inch (100 mm) for most bathroom and utility extract fans. 5-inch (125 mm) or 6-inch (150 mm) for kitchen extractor hoods and MVHR ducting. Boiler and gas-appliance vents are sized per manufacturer instructions — usually 100 mm but sometimes larger.

Can I put a vent in any wall?

External walls — almost always yes, with the caveats above. Party walls (shared with neighbour) — no, you can't vent into someone else's airspace. Internal walls — possible if it's a passive vent between rooms; not for extract because the extract air has to leave the building.

What if my wall is rendered or has insulation?

Rendered walls — the core driller cuts cleanly through, then re-renders the small ring around the vent (£60–£150 extra for matching render). External wall insulation — needs a longer sleeve and careful sealing to prevent thermal bridging; specialist external-wall-insulation installers are best for this case.

Want a local pro to handle this? A core driller or experienced builder will get the vent in straight, sealed, and weatherproof in a couple of hours. The cost difference vs DIY is small once you factor in damage risk on a cavity wall.