Dunedin facts that matter for ventilation
Damp, if a little less than average
EHINZ reports that at the 2023 Census, 16.4% of people in the Southern health district lived in a home that was sometimes or always damp, against 20.6% across New Zealand.
Cold nights, cold roof spaces
In NIWA's 1991 to 2020 normals, Dunedin's July nights average a low of 3.0 degrees. BRANZ says roof space air can be colder than room air at night and on overcast days.
Old brick houses
Heritage New Zealand says most of Dunedin's historic housing is villas from the 1870s on, and predominantly brick.
South Dunedin's groundwater
About 2,700 South Dunedin homes sit less than 50 cm above sea level on soft ground that was once tidal wetland. Otago Regional Council says rising groundwater will eventually bring occasional, and possibly permanent, surface ponding.
Why Dunedin houses get damp, and what ventilation can do
Condensation forms where warm, moist indoor air meets a cold surface, and an old house in a cool climate has plenty of those: single glazing, a chilly back bedroom, a wardrobe on an outside wall.
Ventilation replaces the moist air with drier air, and heating keeps surfaces warm enough that less of it condenses. With 77.68% of Dunedin homes already heating with a heat pump at the 2023 Census, the heating half is often in place.
If the damp comes up from the ground, as it can in low-lying South Dunedin, ventilation only treats the symptom. Get the subfloor and drainage looked at first.
Positive pressure or heat recovery in a Dunedin house?
A villa that still has its timber windows is the kind of house Consumer NZ has in mind for positive pressure, which it rates better in older homes with wooden joinery than in modern ones sealed with aluminium.
The catch is winter: on a frosty night, roof space air may be colder than your rooms, and Consumer NZ says that means turning the heating up. Ask for a controller that slows or stops the fan then.
Balanced heat recovery brings outside air in through a heat exchanger. BRANZ says it's most cost-effective in a relatively airtight building, fitted during a new build or major renovation, and that poor ducting can drag delivered efficiency below 30%. A villa being gutted and relined suits it; a draughty one left as it is is a poorer fit. Our ventilation comparison sets the types side by side.
What makes the job bigger or smaller here
Brick walls. A balanced system needs an intake and an exhaust through a wall or the roof, and brick is more work than weatherboards. Schedule 1 of the Building Act still exempts a hole up to 300 millimetres across in an existing house from building consent.
Storeys and heritage. Duct runs between floors add time. If the house is heritage-listed, Tenancy Services' advice is to check the council's rules first.
Fans first. Kitchen and bathroom extractor fans venting outside cut the moisture load before any system goes in.
What to ask a ventilation specialist
- Where does the supply air come from, and what does the system do on a frosty night?
- Why does this type suit my house rather than the other one?
- How will ducts and vents get through brick, and who makes good afterwards?
- Who's doing the fixed wiring, and will I get a Certificate of Compliance for it?
Yours to do, and not
You can
- Run the bathroom fan through every shower and for a good while after.
- Keep bedrooms warm enough that the windows don't run with water.
- Check from outside that the rangehood and bathroom fan vent outdoors.
Leave to a licensed installer
- All work in the roof space, and the fixed wiring for the fan and controller.
- Cutting holes through brick or the roof, and weatherproofing them.
- Setting the airflows, and balancing supply against extract on heat recovery.
Letting a flat?
The rental ventilation standard wants openable windows, and kitchen and bathroom extractor fans that vent outside. Tenancy Services says recirculating systems, products like HRV and DVS systems included, aren't suitable to meet it.
What we'd do
If it were our house
We'd get the house properly warm and check the kitchen and bathroom fans vent outside. If the windows still run wet after a few weeks, we'd have a ventilation specialist look at the joinery, the roof space and, in South Dunedin, under the floor, before choosing a type. Ventilation specialists see the job, and only the one who takes it gets your details. The national home ventilation page and our Dunedin heating page fill in the rest.