What an Invercargill winter does to a heat pump
Months of heating
NIWA's Southland table gives Invercargill Aero 2,994 heating degree-days a year, peaking at 398 in July. BRANZ says the filter on a heat pump in frequent use should be cleaned several times a year.
Humid air, icy coils
Relative humidity at 9 am averages 85% at Invercargill Aero, and 89% in June and July. Mitsubishi Electric NZ says the more moisture in the air, the more ice forms on the outdoor coil, and more ice means more defrosting.
Gusts and debris
Invercargill averages 109 days a year with gusts over 61 km/h, NIWA says. Wind drives leaves and grit into the outdoor unit's fins, and Mitsubishi Electric NZ says anything compromising airflow compromises performance.
Frosty nights
NIWA says the temperature drops below 0 degrees on 41 days a year on average, so a unit spends many winter mornings working through frost.
Lots of units
At the 2023 Census, 79.63% of Invercargill City homes used a heat pump as a main type of heating.
What makes an Invercargill service bigger or smaller
Time since the last one. A unit that's done two or three winters without a service carries more on its coils and in its drain tray than one seen every year.
Exposure. An outdoor unit on a windward wall, or near the estuary or the coast, collects more salt and grit. Temperzone's yearly maintenance list for Hitachi systems includes clearing lint and dust from the outdoor coil fins and touching up damaged paint to stop corrosion.
Mounting. BRANZ says units should be stable and well maintained, or worn bearings and other parts get noisy. After a season of gusts, brackets and pads deserve a look.
The system. A multi-room system has several indoor units on one outdoor unit, and a ducted one has its unit and filters in the roof space, which takes longer to reach.
What a good service covers here
- Filters and the indoor coil cleaned after a winter of heating.
- The drain tray and hose cleared, with the hose end checked so it isn't sitting in water.
- Leaves, grit and lint cleaned out of the outdoor coil fins.
- Brackets, bolts and the pad checked after the gusts.
- Paint and any corrosion protection inspected, especially near the coast.
- The refrigerant circuit checked for leaks, not topped up as a routine.
- A dated written record you can show a warranty repairer.
Questions worth asking the technician
- Is the outdoor unit icing up more than its spot and the weather explain?
- Are the mounts still tight after the winter's wind?
- Does your service record meet what my brand's warranty asks for?
What you can do between visits
You can
- Clear blown leaves from around the outdoor unit after a storm.
- Clean the filters as the manual says, often through a heavy winter.
- Let the defrost cycle melt any ice on the coil; never chip at it.
Leave to a licensed installer
- Cleaning the coils and drain tray inside either unit.
- Refrigerant leak checks and repairs.
- Electrical faults, and re-fixing loose mounts.
What we'd do
Our take
We'd book in late summer, so the unit goes into Invercargill's long heating months clean and checked. While the warranty runs, we'd keep to the brand's interval to the day. After that, a unit doing this much winter work still earns a yearly visit in our book, especially on an exposed or coastal site. Heat pump servicing specialists see the job, and only the one who takes it gets your details. See our national heat pump servicing page for what each brand asks, and our Invercargill page for the rest of the city.