Range hoods in airtight homes

The problem with standard range hoods

A range hood works by extracting air from the kitchen — pulling it through the hood, through a duct, and exhausting it outside. In a draughty house, this isn’t an issue: replacement air simply leaks back in through gaps and cracks in the building envelope.

In an airtight home, the same process creates a problem. A powerful ducted range hood extracting 400–900 m³/h can depressurise the building significantly. With no easy path for replacement air, the hood’s extraction performance drops, negative pressure builds up, and air is forced in through whatever leakage paths exist — bypassing your filters, your thermal envelope, and your MVHR system entirely.

In homes with wood heaters, gas appliances or clothes dryers, significant negative pressure also creates a risk of backdraught — combustion gases or exhaust air being drawn back into the living space rather than exhausted outside.

What NCC 2022 changed

Since the National Construction Code 2022 came into effect, the rules for kitchen range hoods in new homes are no longer just a matter of best practice — they are mandatory. Under the Housing Provisions condensation-management clause 10.8.2 (Exhaust systems), a range hood installed in the kitchen of a new Class 1 dwelling must discharge to outdoor air — directly, or via a shaft or duct — at a minimum flow rate of 40 L/s.

That single requirement rules out the recirculating range hood — often called a “reticulated” hood — as a compliant kitchen exhaust solution in new builds. A recirculating hood filters the air and returns it to the room; it never discharges outdoors, so it cannot meet the clause. The code also no longer allows kitchen exhaust to be dumped into a ventilated roof space — it has to reach outside.

NCC 2022 goes a step further on the very issue this page is about. Clause 10.8.2 also requires that a kitchen with an exhaust system, where the room is not naturally ventilated, is provided with make-up air — for example an opening with a free area of 14,000 mm² (achievable with a 20 mm undercut to a 700 mm door). In an airtight home that figure is only a starting point: a powerful hood needs a properly sized, sealing make-up air path, not just a gap under a door.

The compliant approach — ducted range hood with make-up air

The solution that meets NCC 2022 and performs in a high-performance home is a conventional ducted range hood, vented outside, paired with a dedicated make-up air supply. When the range hood activates, a controlled supply of fresh air enters the building — through an automated, interlocked damper — replacing exactly the volume of air being extracted.

This keeps the building at neutral pressure, preserves MVHR performance, and allows the range hood to operate at full extraction capacity. The make-up air damper is interlocked with the range hood so it only opens when the hood is running, and a sealing shutter on each penetration stops the wall outlet leaking when the hood is off.

• Discharges outdoors at 40 L/s or more — meets NCC 2022 clause 10.8.2
• Full extraction performance — no compromise on cooking odours, steam or moisture
• Building remains at neutral pressure during hood operation
• MVHR continues to operate normally
• Sealing backdraft shutter prevents air re-entering when the hood is off
• Best practice for Passive House and airtight new builds

Where do recirculating (reticulated) hoods still fit?

A recirculating range hood does not exhaust air outside — it draws air through a grease filter and a charcoal (activated carbon) filter, then returns it to the kitchen. Because no air is extracted from the building, there is no negative-pressure issue and no duct penetration through the envelope. That made it appealing in airtight homes — but in a new build it no longer satisfies NCC 2022.

It can still have a place in a renovation or retrofit that isn’t captured by the provision, or as a secondary appliance, where cutting a new exhaust duct through the envelope is genuinely impractical. Even then, the limitations are real and worth understanding:

For any new home, and for most renovations where it can be achieved, ducted extraction to outside with make-up air is both the compliant and the better long-term solution.

Coordinating with your MVHR system

An MVHR system includes a kitchen extract terminal — but this is designed for background ventilation (continuous low-volume extraction), not for the peak load of active cooking. Do not assume the MVHR extract replaces a range hood; it does not, and under NCC 2022 the range hood itself must discharge outdoors.

If your home has a ducted range hood, it operates as a completely separate system from the MVHR. The two coexist: the MVHR provides continuous background ventilation, and the range hood handles cooking extraction on demand. The key coordination requirements are: