High-wall heat pumps for Dunedin homes

A high-wall is what goes into most Dunedin homes, and three things decide whether it's right for yours: how far up the hill you are, because the cold settles at the bottom; how high the ceiling is, because that's where the warmth collects; and how close to the water you sit.

How much does a high-wall heat pump cost in Dunedin?

Fitted, a bedroom or small room runs about $2,200 to $3,000. A main living area is $3,000 to $4,500, and a large or open-plan space $4,000 to $5,800. That's roughly 2.5kW, 5 to 6kW and 7 to 8kW of capacity.

Those are supply-and-install figures, so they take in the unit, the mounting, the pipework and drain, the electrical connection back to your board, and the vacuum, charge and test at the end. The box price you see advertised covers none of that.

Why the hill shows up on the quote

Two houses with identical rooms can price quite differently here, and the reason is usually the section rather than the house. An outdoor unit that has to be carried up a flight of steps takes two people and longer. A villa through Caversham or Kaikorai often has a long way back to the switchboard, and older boards sometimes have nothing spare on them, which puts a new circuit on the quote.

Out on the Peninsula, at Macandrew Bay or along the coast at St Kilda, a unit built for salt air costs a little more and lasts a great deal longer. Inland and up the hill it makes no practical difference.

The sizing calculator will give you a capacity and a rough figure in a minute, and the installation cost page sets out what moves a quote.

Why the bottom of the hill is colder than the top

Cold air is heavier than warm air, so on a clear, still night it runs downhill and collects at the lowest point it can find. In a city built on hills that has a real consequence: your address decides how cold your mornings actually get, and two houses a few hundred metres apart can be having different winters.

The flat of South Dunedin and the valley floors sit at the bottom of that, so they collect the cold that drains off everything above them and hold it until the sun gets round. A house partway up a sunny slope at Mornington or Maori Hill sheds that cold downhill instead and starts the day several degrees ahead.

It matters because a heat pump takes its warmth from the air outside, and the colder that air is the less there is in it to take. Output drops away as the temperature falls, so the same unit that's comfortable up the hill can be short of the room at the bottom of it on the mornings that count.

That's why the capacity gets worked out for your address rather than your floor plan, and why a neighbour's recommendation is worth less here than it is in a flat city.

Sizing one for a villa with a three-metre stud

Start from 2.5kW for a bedroom, 5 to 6kW for an ordinary lounge and 7 to 8kW for a large or open-plan space. In Dunedin the two things that push a room past that are the ceiling and the glazing.

A high-wall blows warm air out across the room, and warm air rises. With a normal ceiling that's fine, the air circulates and the room evens out. With a three-metre stud in a Central or North Dunedin villa, a good share of what the unit produces collects up above the picture rail and stays there, so the room is being heated from the top down and your feet are last in the queue.

Single glazing does the rest. A pane of glass sheds heat about ten times faster than the wall around it, so a villa front room with the original windows is losing warmth on a frosty night nearly as fast as a modest unit can supply it.

Where the ceiling is genuinely high, a floor console is worth pricing alongside. It sits low on the wall and pushes the heat out at floor level, so it reaches you on the way up instead of after it's gathered at the ceiling. In that particular room it's the better machine, and it's the reason the question comes up so often in this city.

Going big to be safe doesn't solve it either. An oversized unit reaches the set temperature in a rush, cuts out before it has pulled any moisture from the air, and leaves the room warm and clammy.

Where the outdoor unit goes on a hill section

It wants air moving freely round it, a spot up off the ground, and enough room for someone to stand and do the yearly service.

Height off the ground matters more here than in a flat suburb, because the cold that drains downhill pools in exactly the low corners an outdoor unit tends to get tucked into. A unit sitting in a frost hollow starts its morning in the coldest air on the property, spends longer melting frost off itself, and takes longer to get back to heating the house.

The outdoor unit is a copper coil threaded through hundreds of thin aluminium fins, and those fins are how it sheds heat outside. Out on the Peninsula and along the coast, salt settles on them and works into the metal, and once they've corroded there's less left to shed heat through. A coated unit and a position out of the worst of the salt buys it years.

Indoors, the head wants a clear stretch of wall with the room opening out in front of it, blowing down the length of the space rather than straight at where you sit or into a doorway.

Will one heat the whole house?

One in the main living area with the internal doors open covers more of a compact house than you'd think, and for a single open-plan space it's usually all that goes in.

It can't get round a corner or down a hallway, though. Where the bedrooms matter you're choosing between a second unit and a multi-split, which runs two or more indoor heads off one outdoor compressor. On a tight Mornington or Corstorphine section that tidy footprint usually wins, because there's only one outdoor position to solve and one thing to carry up the steps. Out on a spread-out Taieri property there's room for separate systems and the choice opens up again.

For even warmth through a bigger home, ducted runs hidden through the roof space and feeds a vent to every room, and a ceiling cassette recesses into the ceiling and blows down evenly across a large space.

Whichever you fit is reverse-cycle, so it cools in summer as well. Dunedin summers are short, but a north-facing room under the roof still gets uncomfortable, and there's nothing extra to buy for it.

Weighing up the options? Types of heat pump sets a high-wall against a floor console, a ceiling cassette, a multi-split and ducted, and heat pump installation covers the job itself. For a number on your own room, get a free quote.