Healthy Homes Ventilation Standard

Healthy Homes Standard 3 — Ventilation — is one of the mandatory rental standards, and it has two parts. Every habitable room needs windows, doors or skylights that open to the outside, and every kitchen and bathroom needs an extractor fan that vents outdoors. Getting the fan ducted to an external vent (not the ceiling) is the part most people get wrong.

Openable windows in habitable rooms

Habitable rooms are living rooms, dining rooms, kitchens and bedrooms — not bathrooms, laundries or hallways. These rooms need enough that opens to let a tenant actually air the place out.

• The openable area — windows, external doors and skylights that open — must total at least 5% of that room’s floor area.
• Each opening must be able to be held or fixed in the open position, using a stay or catch, so the tenant can leave it open.

Extractor fans in kitchens and bathrooms

A fan is required in any room with a cooktop (kitchen) or a bath or shower (bathroom). The size rules depend on when the fan was installed. For fans installed after 1 July 2019, the minimums are:

• Bathroom: minimum exhaust diameter of 120 mm, or minimum airflow of 25 L/s.
• Kitchen: minimum exhaust diameter of 150 mm (including ducting), or minimum airflow of 50 L/s.

Older fans and the continuous-ventilation alternative

Fans installed before 1 July 2019 are fine as long as they vent to the outside and work — they don’t have to meet the size figures above. There’s also an alternative:

• A continuous mechanical ventilation system can substitute, where the building consent was granted after 1 Nov 2019 and it meets Building Code G4, provided it exhausts at least 12 L/s from the kitchen and at least 10 L/s from the bathroom to outdoors.
• Recirculating systems do not qualify — some HRV/DVS setups that just move inside air around, or a rangehood that filters back into the room. The air must go outside.

Common fail: venting into the ceiling

A bathroom or kitchen fan that vents into the ceiling cavity or roof space instead of through to outside is non-compliant. It also actively causes the moisture and mould problems the standard is meant to prevent. Duct it to an external vent.