Make-Up Air in Airtight UK Homes: What You Need to Know

Every extractor fan removes air from inside the building. In a draughty older home, replacement air trickles back in through gaps around windows, doors, and the building fabric almost as fast as the fan removes it. In a well-insulated modern home, sealed to current building regulations, there are far fewer gaps. Run a powerful cooker hood and you create negative pressure inside the building. The hood works against itself, the extraction rate drops, and in severe cases you get backdraught: air being pulled back down flues, vents, and other openings.

Make-up air is simply the fresh air that needs to enter the building to replace what extraction removes. The question is not whether you need it (you always do), but whether your home provides it naturally or whether it needs help.

Signs the balance is off

Hood feels weaker than expected or becomes noticeably noisier under load
Steam and cooking odours linger despite the hood running
Windows rattle or whistle when the hood or extractor fans are on
Doors are harder to open while fans are running
Backdraught from a fireplace, stove flue, or bathroom fan
Condensation on windows during or after cooking

Any of these suggest the building is not providing enough replacement air to match the extraction rate. The fix is straightforward once the cause is identified.

How homes provide make-up air

Trickle vents Small controllable slots built into window frames, open a few millimetres to allow a continuous low-level airflow. Standard in windows installed since Part F came into force. Keeping them open during cooking is the simplest way to provide replacement air in most homes.

Dedicated wall vents A vent installed through an external wall, usually with a damper that opens automatically when extraction creates negative pressure. More controlled than an open window and does not require the occupant to remember to open anything.

MVHR systems Mechanical ventilation with heat recovery provides continuous balanced ventilation: equal amounts of air in and out. Common in new builds and Passivhaus properties. If your home has MVHR, it is designed to handle make-up air automatically, though very high-output hoods may still need a supplementary path.

Recirculating hood A hood that filters and returns air to the kitchen rather than ducting it outside does not create a net extraction flow, so it does not create a make-up air deficit. It does not remove moisture, but it eliminates the negative pressure problem entirely. Useful in airtight properties where ducting outside is not practical.

Opening a window The most immediate solution and often sufficient for occasional high-output cooking. Not ideal as a permanent strategy in winter, but useful for confirming that negative pressure is the cause: if opening a window immediately improves hood performance, make-up air is the issue.

Does this affect hood choice?

Yes, particularly for high-extraction models. A ducted hood rated at 600 m³/h or above in a well-sealed modern home will create noticeable negative pressure without an adequate make-up air path. This is one reason vented induction hobs with downdraft extraction are well-suited to modern kitchens: the extraction happens at worktop level and the duct route is typically shorter and more direct, reducing the effective pressure difference. It does not eliminate the make-up air requirement, but a shorter, straighter duct path at lower resistance extracts more efficiently at a given fan speed.

Approved Document F sets ventilation requirements for UK kitchens including minimum extract rates and the need for background ventilation (trickle vents or equivalent) in habitable rooms. In airtight new builds, the ventilation strategy must be designed to provide make-up air as part of the overall scheme. The current document is available at gov.uk/government/publications/ventilation-approved-document-f.

For the full picture on kitchen ventilation requirements including when a hood is mandatory and how to size one correctly, see the guides to induction hob ventilation and what size cooker hood you need. For island layouts where make-up air and extraction are both simpler to manage, see the vented induction hob guide.

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