High-wall heat pumps for Invercargill homes

A high-wall is the workhorse down here, and three things decide whether it suits your room: whether the space is open enough for one unit to reach all of it, whether the ceiling is high enough that the warmth will sit above your head, and how much capacity the room needs to hold a temperature through a long, damp winter.

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

Fitted, a bedroom or small room runs about $2,300 to $3,300. A main living area is $3,200 to $4,800, and a large or open-plan space $4,500 to $6,500. That's roughly 2.5kW, 5 to 6kW and 7 to 8kW of capacity.

Those are supply-and-install figures, so they cover the unit, the brackets and mounts, the pipework and drain, the electrical work and the commissioning. A box-only price advertised somewhere isn't a real price, because the fitting still has to happen.

What moves it inside those figures is how hard the job is. It's cheapest when the outdoor unit can sit on the outside of the same wall the indoor head is on. Running the pipework through a cavity, along an outside wall or up to a high mount all add time and materials, and any electrical work at the board adds more.

The number that matters more here

In most of the country the purchase price is the figure people compare. Invercargill is the place where that's least true, because the heating season here is long enough that you'll run the thing for a good part of the year. A unit that's efficient because it was sized properly saves you a little every month for as long as you own it, and over a Southland winter a little every month adds up to considerably more than the few hundred dollars between one model and another.

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

Why the wrong size costs more here than anywhere

A heat pump runs most efficiently when it's working steadily rather than starting and stopping. Getting the size wrong breaks that in one of two ways, and the longer your heating season the more each one costs you.

Too small and it never reaches the temperature you've asked for, so it simply runs. Flat out, for hours, on every cold day of a season that lasts months here, and the room still isn't quite right. You pay for all of that electricity and don't get the warmth.

Too big and the opposite happens. It hits the set temperature in a rush and shuts off, then the room cools and it starts again. Each start draws more power than steady running does, so the bill climbs, and because it's barely running it isn't pulling moisture out of the air. In a climate as damp as this one that's the difference between a room that's warm and one that's warm and still feels clammy.

Neither shows up on the quote. They show up every month afterwards, which is why the sizing is worth more attention here than the brand is, and why it gets measured on site rather than read off a floor plan.

Sizing one for an older villa

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. The question is whether your house pushes that up, and in Invercargill plenty do.

A single-glazed villa through Hawthorndale, Windsor or Richmond loses warmth through the windows and the gaps a great deal faster than a sealed newer place at Rosedale, so the same-sized room wants noticeably more capacity to hold its temperature through an evening.

High ceilings work against a high-wall as well. It blows warm air out near the top of the room and warm air rises, so in a villa with a tall stud a good share of it collects above your head and takes its time coming down. A floor console puts the same heat in at floor level instead, so it reaches you on the way up, and in that kind of room it does the job better for similar money.

A draughty hallway changes the answer too, because it turns one room into several and a high-wall can't heat round a corner.

Where the outdoor unit goes

It wants a solid base off the ground, air moving freely around it, and enough room for someone to get at it for the yearly service.

Out of the worst of the southerly matters here. Wind blowing straight into the front of the unit drives more damp air across it, and in heating mode the metal on the back of it is already below freezing, so frost builds faster and it stops more often to melt it off. Every one of those is a few minutes when it isn't 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 at Otatara and down toward Bluff there's salt in the air, and it settles on them and works into the metal until there's less left to shed heat through. A coated unit costs a little more and lasts a lot longer on those addresses.

Indoors, the head wants a clear stretch of wall with the room opening out in front of it. Aimed into a doorway or across the back of a sofa it warms the air right around itself, decides the room is up to temperature and backs off.

Will one heat the whole house?

For a single open living space, one in the main room usually is the whole job, and with the internal doors open it reaches further than people expect.

It won't push warmth around a corner or down a long hallway on its own, though. Where you want bedrooms done as well, a multi-split runs two or more indoor heads off a single outdoor unit, and you can mix the styles on it, so a high-wall in the lounge and a floor console in a cold bedroom run off the same outdoor box.

For the whole house out of sight, ducted hides in the roof and feeds warm air to each room through vents, and a ceiling cassette sits flush in the ceiling and blows out several ways across a large room.

Whatever goes in also cools and dehumidifies, and in Southland the second of those earns its keep long after the cooling stops being useful.

Not settled on a style yet? Types of heat pump compares a high-wall with a floor console, a ceiling cassette, a multi-split and ducted, and heat pump installation walks through the job. For a number on your own room, get a free quote.