Does your house need a ventilation system?
Damp is common here. EHINZ reports that in the 2023 Census, 20.6% of people lived in a dwelling that was sometimes or always damp, and that 16.5% lived where mould bigger than an A4 sheet of paper showed up at least some of the time.
Streaming windows on winter mornings, a musty wardrobe and black spots on the ceiling are the usual signs. Check the basics first: a bathroom extractor fan and a rangehood that both vent outside remove a lot of moisture at the source.
If it's still damp after that, a ventilation system is the next step. It won't warm the place, though: BRANZ says heat recovery systems aren't heating systems, and Consumer NZ warns that blowing roof space air in during winter means turning your heating up.
Positive pressure or balanced heat recovery?
| Positive pressure | Balanced heat recovery | |
|---|---|---|
| Where the air comes from | The roof space, or outside in some types, Consumer NZ says | Outside, drawn in by its own fan |
| How stale air leaves | Pushed out through gaps, doors and windows | A second fan extracts it through ducts |
| Winter nights | BRANZ says roof space air can be colder than your rooms | Incoming air picks up heat from outgoing air |
| Suits | Older houses with wooden joinery, Consumer NZ says | Modern, relatively airtight homes |
| Building Code clause G4 | BRANZ says roof space air isn't fresh outdoor air | BRANZ says it meets the fresh outdoor air requirement |
HRV and DVS are companies, not types
HRV and DVS are the names of two businesses that sell ventilation systems. Being quoted 'an HRV' tells you who makes it, not how it works, so ask whether it's positive pressure or balanced heat recovery. For anything sold as heat recovery, BRANZ's advice is to make sure the system actually includes a heat recovery device. Our ventilation comparison sets the types side by side.
What the job involves
A ventilation specialist starts with the house, not the brochure. They'll check the roof space for safe access, insulation and room for the fan unit, then look at your joinery, draughts and where the moisture comes from. That visit is when they should tell you which type suits, and why.
On the day, the fan unit and ducts go into the roof space, outlets go into the ceilings, and a controller goes on an inside wall. A balanced system adds extract ducts, the heat exchanger, and an intake and exhaust outside.
What makes the job bigger or smaller?
Type matters most. A positive pressure system is one fan unit and a handful of outlets. A balanced system has two duct networks, and BRANZ says its delivered efficiency can fall below 30% if duct heat and air losses aren't properly considered, so the design takes real care.
Then it's the house: how many rooms need outlets, how easy the roof space is to work in, how far the ducts run, and whether the air comes from the roof or outside. BRANZ says balanced heat recovery makes most sense in a relatively airtight building, fitted during a new build or a major renovation.
Who can legally do which part?
The wiring is the licensed part. Fixed wiring for the fan unit or controller is prescribed electrical work, which only a registered and licensed electrical worker can carry out or supervise, and they owe you a Certificate of Compliance no later than 20 days after finishing.
A duct hole through the wall of an existing house needs no building consent if it's no more than 300 millimetres across: Schedule 1 of the Building Act 2004 covers it, weatherproofing included. All building work still has to meet the Building Code. In a unit title, read the body corporate's rules before anyone touches the roof or outside walls.
Renting? The ventilation standard is about fans and windows
Rentals need openable windows in the main rooms, plus extractor fans that vent outside in the kitchen and bathroom. Tenancy Services says recirculating systems, products like HRV and DVS systems, aren't suitable to meet the standard, so they don't replace those fans.
The exception: in a home whose building consent was first received on or after 1 November 2019, a continuous mechanical ventilation system can stand in for the fans if it continuously extracts air from the kitchen and bathroom to the outdoors. That's for the landlord to check.
What's yours to do, and what isn't
You can
- Run the bathroom extractor fan while you shower and for a while after.
- Use the rangehood whenever you cook, and check it vents outside.
- Wipe condensation off the windows each morning, and note which rooms are worst.
- Change filters yourself only if the manual shows they're reachable from inside the house.
Leave to a licensed installer
- Anything in the roof space: the fan unit, ducts and roof space filters.
- Fixed wiring for the fan and controller, and the Certificate of Compliance.
- Cutting ceiling outlets and wall holes, and weatherproofing them.
- Setting the airflow, and matching supply to extract on a balanced system.
What to ask before you say yes
- Where will the air come from: the roof space, or outside?
- If it's sold as heat recovery, where's the heat exchanger?
- What does the controller do when the roof space is colder than the house?
- Which filter grade is fitted, and how often will it need replacing?
- Who does the wiring, and when will I get the Certificate of Compliance?
What we'd do
Where we'd start
We'd sort the obvious moisture first: extractor fans that work and vent outside, and enough heating to keep the house properly warm. If the windows are still running wet after a few weeks of that, we'd get a ventilation specialist to look at the house before choosing a type. In an older villa with timber joinery, that's often positive pressure; in a newer, tighter home, more likely balanced heat recovery. Either way, we'd want the reason written on the quote, not just a model name.