Heat pumps for Mosgiel, Outram and the Taieri

Mosgiel and Outram sit on the flat Taieri plain, ringed by hills that let cold air drain down onto them and pool overnight. On a clear still night the plain runs several degrees below the city, and hard ground frost is routine rather than remarkable. A unit specified on Dunedin averages will disappoint its owner every July.

Why the plain runs colder than the city

Cold air is heavy. On a clear still night it slides off the surrounding hills and settles on the flat, and with nothing to stir it the temperature keeps dropping until dawn. The coast a few kilometres away stays milder because the sea moderates it; the plain has no such help.

That is why the frost here is genuine rather than a light dusting, and why it forms on nights the city does not get one. The practical consequence is that the heat pump is working at its hardest exactly when you most want it, so what matters is the output at around 2 degrees, not the headline figure measured at 7.

Fog is the other half of it. The Taieri fogs in readily and it can sit all morning, keeping everything damp and making the house feel colder than the thermometer says.

Specifying for real frost

Ask your installer directly what the unit does at low ambient temperatures and whether it holds its rated output or tapers off. Cold-climate models keep working further down the scale, and out here that is worth the difference rather than a nice-to-have.

Defrost cycles are the other consideration. On a frosty Taieri morning the outdoor unit will ice up and run a defrost several times, steaming for a few minutes each time before normal heating resumes. That is the unit working correctly, not a fault, but it does mean the outdoor unit has to drain properly. A unit sitting where meltwater pools and refreezes each night will not last.

The sizing calculator is a reasonable starting point, and the installation cost page has the ranges by unit size.

Bigger sections, easier installs

Mosgiel and Outram are mostly post-war and later housing on generous flat sections: brick-and-tile, larger family homes, and a steady run of newer subdivision building around Mosgiel.

That makes the physical install far easier than on a steep city section. There is usually a sheltered spot with room to breathe around the outdoor unit, no steps to carry it up, and space for extra pipework if the best indoor position calls for it. Whole-home options are more practical here too: where the roof space allows it, ducted heat pumps suit the larger single-level houses better than three or four separate high-walls.

Newer builds around Mosgiel are well insulated and tighter, and generally need less capacity than owners expect. The frost still applies; the heat loss does not, so the two pull in opposite directions and the sizing is worth doing properly.

Living with it out here

Run it steadily through the cold snap rather than switching it on and off. A house on the plain loses its warmth quickly once the unit stops on a frosty night, and recovering from cold costs more than holding a steady temperature does.

Keep the outdoor unit clear of long grass and shrubs, make sure the defrost meltwater can get away from it, and have it looked over every year or two. The defrost cycle works a unit harder here than in the city, so regular heat pump servicing earns its keep. The heat pump installation page covers how the job runs from the first visit.

Suburbs covered in Mosgiel, Outram and the Taieri

• Mosgiel
• Outram

Somewhere else around the district? Your local installer also covers Central Dunedin and the hill suburbs, Otago Peninsula and the beaches and South Dunedin and the flat. The full list is on the areas we serve page, or get a free quote for your place.