Healthy Homes Ventilation Standard NZ: Extractor Fans, Ducting and Window Rules

Two Types of Ventilation: Natural and Mechanical

The ventilation standard has two parts. Every liveable room needs adequate natural ventilation through openable windows. Kitchens and bathrooms with specific fixtures need mechanical extraction — fans that pull moist air out of the building entirely.

Getting either wrong is one of the most common compliance failures, particularly because older extraction systems often vent into the roof space rather than outdoors.

Natural Ventilation: The 5% Rule

Every liveable room — bedrooms, living rooms, dining areas, and kitchens — must have openable windows, doors, or skylights. The total openable area must equal at least 5% of the room's floor area.

For a bedroom measuring 12 square metres, that means at least 0.6 square metres of openable window area. Measure the actual openable section of each window (not the full frame), and add them up.

All openable windows must also be capable of being fixed in an open position. A sash window that slides shut under its own weight unless propped does not meet this requirement.

Mechanical Extraction: Kitchen Requirements

Any kitchen with an indoor cooktop needs a mechanical extraction system — either a rangehood or an extractor fan — that meets these specifications for systems installed after 1 July 2019:

• Minimum ducting diameter: 150 mm (both the fan unit and the ducting)
• Minimum exhaust flow rate: 50 L/s (180 m³/h)
• Must discharge directly outdoors — through an external wall vent or roof penetration

A recirculating rangehood — the kind that filters air and blows it back into the kitchen — does not satisfy the standard. It must extract air and send it outside.

Mechanical Extraction: Bathroom Requirements

Any bathroom with a bath or shower needs mechanical extraction meeting these specs (post-1 July 2019):

• Minimum ducting diameter: 120 mm
• Minimum exhaust flow rate: 25 L/s (90 m³/h)
• Must discharge directly outdoors

If your bathroom fan vents into the roof space, the subfloor, or a wall cavity, it is non-compliant. This is the single most common ventilation failure. Moisture dumped into the roof space causes timber rot, mould in the insulation, and condensation problems that compound over time.

Pre-2019 Fans: A Different Standard

Extraction systems installed before 1 July 2019 have a simpler requirement: they must be in good working order and extract air directly outdoors. No minimum ducting diameter or airflow rate is specified for legacy systems.

This means a small, old bathroom fan with 100 mm ducting that still works and vents outdoors is technically compliant. But if you replace it with a new unit, the new installation must meet the full post-2019 specifications.

Continuous Ventilation Systems

Some properties use multi-room continuous mechanical ventilation systems instead of individual extract fans. These are compliant if they deliver at least 12 L/s in the kitchen and 10 L/s in the bathroom continuously.

Positive-pressure ventilation systems (like DVS or HRV ceiling-mounted units) that push filtered air from the roof space into living areas do not satisfy the mechanical extraction requirement. They move air around the house but do not extract moisture-laden air from kitchens and bathrooms to the outside.

How to Check and Document

1. Turn on each extractor fan and hold a sheet of tissue paper near it — if it pulls the tissue firmly, the fan is working. If you can feel barely any suction, the fan may be blocked, the ducting may be crushed or disconnected, or the motor may be failing
2. Trace the ducting from the fan to its exit point. Confirm it exits through an external wall or roof — not into the attic or subfloor
3. Check the duct for kinks, tears, crushing (especially where it passes through tight framing), or disconnections at joints
4. Measure or note the ducting diameter from the product spec sheet or by measuring the duct itself
5. Record the fan make, model, and rated airflow (often printed on the unit or in the product manual)
6. Photograph the fan, the ducting run, and the external vent

The NZ Healthy Homes compliance guide includes a room-by-room ventilation measurement sheet and the specifications to hand to an electrician if you need a fan replacement or ducting upgrade.

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