Wellington summers, by the numbers
Few hot days
NIWA calls Wellington the least extreme of the region's main stations. February days average a high of 20.6 degrees at Kelburn and 21.2 at the airport, on 1991 to 2020 normals via Wikipedia.
A small cooling need
Wellington Aero logs 80 cooling degree-days a year against 1,625 for heating. NIWA adds that low coastal sites get more cooling degree-days than inland ones, so a harbourside flat may want cooling more than a house further inland.
Sunny in places
NIWA says the south-western tip of the region is its sunniest part, with more than 2,100 hours of bright sunshine a year. A north or west facing room full of glass can still overheat on a calm, clear day.
Neighbours close by
With 30,390 Wellington City households in flats, townhouses and apartments at the 2023 Census, plenty of outdoor units sit within earshot of a neighbour.
Is cooling worth planning for here?
For most Wellington homes, it's a check rather than a plan. Buy the heat pump for winter, then confirm its cooling capacity at 35 degrees on the label covers the room. BRANZ says cooling capacity is generally about 10 to 20% below heating capacity, so look at the number rather than assume.
The exceptions are rooms that trap heat: a top-floor apartment, a glassed-in sunroom, a west-facing lounge. If the unit will mainly cool, EECA says to size it on the 35 degree cooling capacity and to allow for window size and orientation, insulation and shading.
Muggy rather than hot? Running a heat pump in dry mode pulls some moisture out, Consumer NZ says, but a purpose-built dehumidifier does it better. In Dry mode, Mitsubishi Electric NZ says, the unit isn't heating.
Placing the outdoor unit for summer nights
Cooling tends to run on warm evenings, when windows are open. Noise limits are set in the district plan and we don't have Wellington's figures to quote, so follow BRANZ and keep the outdoor unit away from bedrooms, yours and the neighbours'.
In a unit title, the body corporate may have to agree before an outdoor unit goes on common property. Ask before you collect quotes.
Cooling also produces water at the indoor unit. BRANZ says that hose belongs in a drain or garden, not on a path or a neighbour's deck.
Questions if a room overheats
- Is the cooling capacity at 35 degrees enough for this room?
- How many blue stars does it get in the Cold zone?
- What outdoor noise figure does the label show, if any?
- Can the outdoor unit go away from the neighbours' bedrooms?
- Would blinds or shading fix it instead?
Try these before buying for cooling
You can
- Draw curtains or blinds on the sunny side before the room heats up.
- Use Cool rather than Auto in summer, as Mitsubishi Electric NZ suggests.
- Clean the filters before summer.
- In a unit title, check the body corporate rules.
Leave to a licensed installer
- Sizing for the room's glass, sun and insulation.
- Refrigerant pipework and commissioning.
- The electrical connection and the Certificate of Compliance.
- Routing the condensate drain.
What we'd do
Our honest take
In Wellington, we'd buy for winter and treat cooling as a bonus, unless one room is genuinely hard to live in on a sunny afternoon. For that room, we'd size on the 35 degree cooling figure and put the outdoor unit where it won't bother anyone at night. And if shading would solve it, we'd try that first.