Most bedrooms suit a small unit of around 2.5–3.5 kW, typical living rooms around 5–6 kW, and large open-plan spaces 7 kW or more. The right size depends on the room, not just the floor area, so treat these as starting points and confirm with a proper assessment.
In this article5 sections
Choosing a heat pump by price or by what a neighbour has is the most common mistake we see. The right size depends on the room it's heating and how that room holds onto warmth. Get it right and the unit runs quietly at a steady pace. Get it wrong and you'll notice every frosty morning.
Why size matters
Too small and the heat pump runs flat out for hours, still doesn't reach the temperature you set, and costs more to run than it should. On the coldest Waikato mornings, when the outdoor unit has to work hardest, an undersized system is the first to give up.
Too big and you pay more upfront for capacity you don't use. An oversized unit also tends to blast the room warm and then idle, which can feel uneven and less comfortable than a correctly sized one ticking over.
What decides the size
- Room size and ceiling height. It's the volume of air that matters, so a 2.7 m stud or a raked ceiling needs more than the floor area suggests.
- Insulation. Ceiling and underfloor insulation make a big difference. An older, uninsulated home can need noticeably more capacity for the same room.
- Windows. Large areas of single glazing lose heat quickly; double glazing and good curtains help the heat pump keep up.
- Sun. A north-facing room that gets afternoon sun is easier to heat than a shaded south-facing one.
- Open-plan spaces. If the lounge opens into the kitchen, dining room or a hallway, the heat pump is heating all of it. Size for the whole connected space.
- How cold it gets. Hamilton and the wider Waikato regularly get winter mornings below zero. A heat pump's output drops as it gets colder outside, so we size with those mornings in mind, not an average day.
- What it's for. Is it the main heating for the house or a top-up for one room? Main heating needs more margin.
Typical starting points
These are heating capacities for a reasonably insulated home. They're a guide, not a quote:
- Bedroom or small office: around 2.5–3.5 kW.
- Average living room: around 5–6 kW.
- Large or open-plan living area: 7 kW and up, sometimes more than one unit.
- Whole home: a ducted or multi-room system is often the better answer than several separate wall units.
Check the heating figure, not just the name
Heat pumps are usually named by their cooling capacity, but in New Zealand it's heating you care about. A unit sold as "5 kW" might deliver 6 kW of heat. Always compare the heating capacity, and ask how it performs when it's cold outside.
Get an estimate in a minute, then confirm it
Our free heat pump sizing calculator gives you a ballpark size from a few quick questions. For a fixed-price quote, we come out, measure the rooms, check the insulation, glazing and ceiling space, and recommend the size that suits the way you'll use it. The assessment is free and there's no obligation.
Frequently asked questions
What size heat pump do I need for a living room in NZ?
An average living room usually suits a heat pump with around 5–6 kW of heating capacity. Large or open-plan living areas often need 7 kW or more. Insulation, ceiling height, glazing and how cold your mornings get all change the answer, so confirm it with an in-home assessment.
What size heat pump do I need for a bedroom?
Most bedrooms and small offices suit a small unit of around 2.5–3.5 kW heating capacity.
Is it better to oversize a heat pump?
No. A heat pump that is too big costs more to buy and tends to blast heat and then idle, which is less comfortable. A correctly sized unit runs steadily and efficiently.
Ready for a comfortable home all year?
Book a free in-home assessment and get a fixed-price written quote from our local team in Hamilton, the Waikato and Auckland.