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.

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Sizing calculator

What size heat pump do you need?

Answer six questions about your room. Takes about 60 seconds.

Room type

Floor area

Ceiling height

Insulation

Orientation

Windows

What type of room are you heating?

This affects usage pattern and how we recommend the unit type.

Bedroom

Master, double, or single bedroom

Lounge / living area

Main living or family room

Open plan

Combined kitchen, dining, lounge

Office / study

Workspace or study room

What's the floor area?

Length × width. For open-plan areas, use the full combined area.

18 m²

Medium bedroom / office

8m² 80m²

What's the ceiling height?

Higher ceilings mean more air volume to heat — affects capacity needed.

Standard

Up to 2.4m — most homes

Medium

2.4 – 2.7m

High

2.7m or above

How well insulated is the room?

Insulation significantly affects how quickly heat escapes — and how hard the unit has to work.

Poor

Pre-1980s, little or no insulation

Average

Some insulation, 1980s–2000s

Good

Well insulated, newer build

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.

North

Gets most sun

East

Morning sun

West

Afternoon sun

South

Least sun

How much glazing (windows) does the room have?

Large single-glazed windows lose substantial heat. Double glazing significantly reduces this.

Small windows

Single glazed

Large windows

Single glazed — older home

Double glazed

Any window size

— kW

Estimated capacity range

Suggested type

—

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.

Call 09 242 4940 for a precise assessment

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.

Heat pump sizing calculator — get the right kW range

Get a free quote

What size heat pump do you need?

Getting it wrong costs you either way

Six factors that determine the right size

Common questions about sizing

Ready for a precise assessment?