Heat pump sizing calculator for Dunedin homes

A rough starting point is about 0.15 kW per square metre for a well-insulated room, but older Dunedin villas with single glazing and high ceilings often need closer to 0.2 kW to handle mornings near freezing. Get the number checked before you buy.

What a sizing calculator actually needs to know

Floor area on its own doesn't tell you much. The same 30 square metre lounge in a modern Mosgiel townhouse and a draughty St Clair villa needs two different heat pumps. A calculator that only asks for square metres is guessing.

To get close you need the room's floor area, ceiling height, how many outside walls it has, the window size and whether they're single or double glazed, and how much insulation is in the walls and ceiling. Aspect matters too, a south-facing hill room that never sees sun loses heat all day.

• Floor area and ceiling height (villas with 2.7 metre studs need more)
• Number of external walls and how exposed the room is
• Window area and single or double glazing
• Wall and ceiling insulation, or the lack of it
• Which way the room faces and how much sun it gets

Why Dunedin villas need more grunt than the online numbers suggest

Most national sizing charts assume a mild average and a reasonably tight, insulated home. That doesn't describe a lot of Dunedin housing. Single-glazed villas with minimal wall insulation and high ceilings leak heat fast, and a unit sized off a generic chart will run flat out and still leave the room cool on the coldest mornings.

We size for the genuinely cold days, not the average. Frost-prone flats out on the Taieri around Outram, and the cold valley and hill pockets around Halfway Bush and Kaikorai, all sit colder than the city figure. If you buy a heat pump that copes with a mild day, you'll be disappointed in July.

Sizing one room versus heating the whole house

A single high-output unit is the usual pick for an open-plan living area. But if you want warmth reaching bedrooms and a hallway as well, one big head in the lounge won't push heat around corners. That's where multi split heat pumps come in, one outdoor unit feeding several smaller indoor heads, each sized for its own room.

Which way you go changes the sizing sums and the price. It's worth looking at the types of heat pump before you settle on a number, because a high-wall, a floor console and a ducted system all suit different rooms and different villas.

Get the figure confirmed before you commit

A calculator gets you a ballpark so you're not going in blind. But we won't quote off it alone. We come out, measure the rooms, look at the glazing and insulation, and check where the outdoor unit can go. That's how you avoid paying for a unit that's over or undersized.

Once we've measured up, we'll give you a straight figure on the heat pump installation cost and talk you through the heat pump installation in Dunedin itself, so you know what the day looks like before you say yes.