Indicative estimate — free on-site assessment available
Heat pump sizing calculator — get the right kW range
Enter your room details below and get an instant kW estimate. It accounts for room size, ceiling height, insulation, orientation, and windows. Good for initial planning — we do the precise calculation on-site before recommending a model.
Sizing calculator
What size heat pump do you need?
Answer six questions about your room. Takes about 60 seconds.
What type of room are you heating?
This affects usage pattern and how we recommend the unit type.
What's the floor area?
Length × width. For open-plan areas, use the full combined area.
What's the ceiling height?
Higher ceilings mean more air volume to heat — affects capacity needed.
How well insulated is the room?
Insulation significantly affects how quickly heat escapes — and how hard the unit has to work.
Which direction does the main window face?
North-facing rooms get passive solar heat gain. South-facing rooms lose more heat and get less sun.
How much glazing (windows) does the room have?
Large single-glazed windows lose substantial heat. Double glazing significantly reduces this.
— kW
Estimated capacity range
Suggested type
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This is an indicative estimate only. It accounts for the main sizing factors but can't replace a proper heat load calculation on-site. Actual requirements vary with your home's specific construction, air leakage, and microclimate. We do precise calculations free of charge as part of every installation assessment — the estimate here is a useful starting point, not a final specification.
Why size matters
Getting it wrong costs you either way
Both undersized and oversized units create problems — and neither is a cheap fix once installed.
Undersized unit
Runs at full capacity constantly — wears out faster
Can't reach set temperature on cold nights
Higher running costs — always working flat out
Constant noise as it struggles to keep up
Uneven temperatures across the room
Oversized unit
Short-cycles — turns on and off constantly
Never runs long enough to properly dehumidify the air
Higher upfront cost for capacity you don't need
Each startup wastes energy — efficiency suffers
Can make the room feel stuffy and humid
What we assess on-site
Six factors that determine the right size
Room area is just the starting point. These are the factors we measure during a proper site assessment — all of which the calculator above accounts for in simplified form.
Floor area and volume
Total floor area multiplied by ceiling height gives the air volume that needs heating. High stud homes need meaningfully more capacity for the same floor area.
Insulation levels
The single biggest variable after room size. A poorly insulated 1960s home requires significantly more capacity than a modern well-insulated room of the same dimensions.
Orientation and sun
North-facing rooms with good sun gain can need 10–15% less capacity. South-facing rooms with no solar gain need correspondingly more to compensate.
Window area and type
Single-glazed windows are one of the biggest sources of heat loss in older South Auckland homes. Large single-glazed windows can increase sizing requirements noticeably.
Air leakage
Gaps around doors, windows, and building penetrations let cold air in and heated air out. Older homes typically have more air leakage than newer ones — assessed on-site.
Occupancy and use
A bedroom used only overnight has different requirements to a lounge occupied all day. How you use the space, and at what temperature, affects the final specification.
Sizing questions
Common questions about sizing
The sizing questions we get asked most often.
Can I just use a rule of thumb like 1kW per 10m²?
Those old rules were rough guides for a simpler era of heating equipment. Modern heat pumps are sized using heat load calculations that account for insulation, glazing, orientation, ceiling height, and air leakage. A poorly insulated south-facing room might need twice the capacity of a well-insulated north-facing room of the same floor area. The calculator above is more accurate than a per-m² rule — but still not as precise as an on-site assessment.
Should I go bigger just to be safe?
No — this is one of the most common and expensive sizing mistakes. An oversized unit short-cycles constantly, never runs long enough to properly dehumidify the air, and costs more upfront for capacity you don't use. A correctly sized unit that runs consistently is more efficient, more comfortable, and lasts longer.
I'm planning to add insulation after installation — should I size for before or after?
Tell us about the planned insulation before we size the unit. If you improve insulation after installation, you may end up with an oversized heat pump — which causes all the problems described above. We can size for the improved insulation state if you're confident the upgrade will happen within a reasonable timeframe.
Does the calculator account for open-plan rooms that connect to other areas?
Partially — selecting "open plan" as the room type adds a load factor. But if your open-plan area opens into hallways or other rooms through doorways that are frequently left open, the effective heated area is larger. For complex layouts, the on-site assessment is more reliable than any calculator.
How do I know if my home is poorly, averagely, or well insulated?
A rough guide: homes built before 1978 typically have little or no insulation (poor). Homes built between 1978 and 2000 typically have some ceiling insulation but limited wall and floor insulation (average). Homes built after 2000 typically meet better insulation standards (good). If you're unsure, select average — it's the most common situation in South Auckland's housing stock. We assess this during the site visit.