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Notes on how to think about sizing a heat pump
Room size and volume • Square metres of the room • Ceiling height (higher ceilings mean more air volume to condition) • Insulation quality • Ceiling, wall, and underfloor insulation levels • Window type (single vs double glazing, low-E glass)
Local climate • Average winter and summer temperatures • Humidity and frost conditions (important for Northland vs South Island in NZ)
Room orientation • North/south/east/west facing (affects sun exposure and heat gain/loss) • Shading from trees, eaves, or neighbouring buildings • Number of external walls • More external walls = more heat loss/gain, requiring higher kW output • Air leakage / draughts • Door gaps, chimneys, or older wooden joinery can reduce efficiency
Intended use • Living areas vs bedrooms (living rooms usually need higher kW capacity) • All-day use vs spot heating/cooling • Open-plan vs enclosed rooms • Open layouts require larger units to condition connected spaces • Hallways and doorways may reduce effectiveness
Occupancy levels • More people generate body heat but also increase cooling needs in summer • Appliances and lighting • Kitchens and rooms with high appliance loads may need extra cooling capacity • Desired heating/cooling speed • Larger units can heat/cool quickly, but oversizing can cause short cycling and reduced efficiency
Noise considerations • Higher kW units can be louder indoors and outdoors • Future needs • Whether the space will be renovated, extended, or used differently in coming years • Power supply capacity • Electrical wiring and switchboard limits may affect the maximum unit size possible