Invercargill facts an installer should design around
Climate zone 6
MBIE's H1/AS1 Acceptable Solution (sixth edition) puts Invercargill City in zone 6, the same zone as Queenstown-Lakes District.
Sub-zero nights
NIWA counts 41 days a year when the minimum drops below 0 degrees, and Invercargill's coldest on record is -9.0.
Wet air on the coil
With NIWA's 9 am humidity averaging 89% in June and July, there's plenty of moisture to freeze onto an outdoor coil on a cold night.
Westerly gusts
Gusts pass 94 km/h on 15 days a year, and NIWA notes the city's high share of strong westerlies, partly funnelled through Foveaux Strait.
Sizing for Invercargill nights
EECA says to size a mainly-heating unit on its 7 degree capacity and, where nights get to 2 degrees or lower, to make sure the 2 degree capacity is no smaller. Here, that's the number that counts.
Mitsubishi Electric NZ says sub-zero areas like most of the South Island need a larger capacity heat pump or one of its upgraded models. Rinnai NZ says it doesn't exclude its heat pumps from colder climate zones, but won't promise heating performance below zero. Read each brand's own words, and Consumer NZ's low temperature performance scores, before choosing.
BRANZ's rough rule is 65 W per cubic metre of room volume for an older uninsulated house, and 50 to 55 for a newer well-insulated one. Heat pumps don't replace insulation, it adds, so check the ceiling and underfloor first. Our size calculator is a good start.
Where the outdoor unit should go
BRANZ wants at least 500 mm clear in front of the coil's air inlet and outlet, 100 mm on the other sides and 100 mm off the ground, ideally on a warm north or west facing wall. With Invercargill's westerlies, ask whether a north wall gives you the warmth with more shelter.
Mitsubishi Electric NZ calls the outdoor unit's location essential for low temperature performance, and says units under houses or decks can create their own microclimate. BRANZ says the indoor unit's condensate hose should run to a drain or a garden, not onto a path, and a wet path on a frosty morning turns to ice.
Near the coast, ask about corrosion protection. Black Diamond Technologies, which issues Mitsubishi Electric's NZ warranty, says units in coastal environments must be assessed and protected before installation, and its warranty excludes issues from outdoor units close to neighbouring boundaries.
What makes the job bigger or smaller
Replacing a burner. Ask who removes the old burner and makes good the flue opening. It isn't heat pump work, so it may be a separate trade.
More rooms. Heating the bedrooms too can mean a multi-room heat pump or several single units.
Pipe runs. BRANZ and Mitsubishi Electric NZ both say to stay within the maker's recommended pipe run lengths, and a high bracket on an exposed wall takes more fixing than a pad in a sheltered corner.
Who signs off what
A registered and licensed electrical worker makes the connection, because it's prescribed electrical work. Their Certificate of Compliance is due no later than 20 days after the work, and WorkSafe's form says to keep the Electrical Safety Certificate for at least 7 years. A pipe hole up to 300 millimetres across through an existing house needs no building consent under Schedule 1, though the Building Code still applies; we don't hold Invercargill City Council's own position, so ask it about anything unusual.
Ask before you say yes
- What's the heating capacity at 2 degrees, against the 7 degree figure?
- Why this outdoor spot, and how will it be fixed down against the gusts?
- Where will the drain water go on a frosty morning?
- Does my site need corrosion protection, and is it on the quote?
- Is this a quote or an estimate?
Before the installer arrives
You can
- Measure the room, including the ceiling height.
- Note how far a possible outdoor spot is from a neighbour's bedroom.
- Compare the 2 degree heating figures on every label you're shown.
Leave to a licensed installer
- Heat loss and sizing for your rooms.
- Refrigerant pipework and charging.
- The electrical connection and its Certificate of Compliance.
What we'd do
If it were our home
We'd choose on the 2 degree heating figure, put the outdoor unit on a sheltered north wall if the house allows, and get the corrosion question answered in writing anywhere near the coast. Installers who specialise in heat pump installation see the job, and only the one who takes it gets your details. Our national heat pump installation page and our Invercargill page cover the rest.