Heat Pump Installation Guide: Sizing and Placement NZ

Heat pumps have become the heating system of choice for New Zealand homes, and with good reason. They are dramatically more efficient than traditional heaters, provide both heating and cooling, and modern units are quieter and more capable than ever. Yet many homeowners end up with heat pumps that underperform, run constantly without warming the space, or cost more to operate than expected.

The problem is rarely the heat pump itself. Most issues trace back to incorrect sizing, poor placement, or both. Getting these fundamentals right from the start makes the difference between a heat pump you love and one that disappoints.

Understanding Heat Pump Sizing

Heat pump capacity is measured in kilowatts (kW), and choosing the right size involves balancing the space you need to heat against the conditions that make heating more or less challenging. Too small, and the unit will run constantly without adequately warming your space. Too large, and it will cycle on and off frequently, reducing efficiency and increasing wear.

• Small rooms: capacity still depends on volume, insulation, glazing, climate and layout
• Medium rooms: obtain a room-specific capacity assessment
• Large or open-plan areas: airflow and zoning can matter as much as floor area
• Very large or multi-room spaces: compare single-split, multi-split and ducted designs with an installer

These figures assume standard ceiling heights around 2.4 metres and moderate insulation. However, many factors can push requirements higher: high ceilings, large window areas, poor insulation, exposed locations, or particularly cold regions all increase heating demand. Conversely, well-insulated modern homes with double glazing may need less capacity than the square metre figures suggest.

Why Bigger Is Not Better

A common mistake is choosing an oversized heat pump thinking it will heat faster or handle extreme conditions better. This approach backfires. Heat pumps work most efficiently when running at moderate output levels for extended periods. An oversized unit quickly reaches the target temperature, then shuts off. A few minutes later, as temperature drops, it starts again. This constant cycling is inefficient and wears components faster.

Properly sized heat pumps run longer cycles at lower intensity. They maintain more consistent temperatures, operate more quietly, and cost less to run. The ideal unit handles your normal heating needs on medium settings, with reserve capacity for particularly cold days.

• Undersized: Unit runs constantly but struggles to maintain temperature, especially on cold days. Room never quite feels warm enough.
• Oversized: Unit frequently cycles on and off. Temperature swings between too warm and too cool. Power bills higher than expected.
• Correctly sized: Unit runs for extended periods at moderate fan speeds. Maintains consistent temperature without constant cycling.

Placement Fundamentals

Where you install your heat pump matters almost as much as which one you choose. EECA says the indoor unit should generally be installed high on an exterior wall, away from corners, with placement chosen to distribute air through the occupied space. This allows heat to circulate naturally and reach the areas where you spend time.

External-wall penetrations need careful weathertight and structural treatment. Auckland Council recommends professional advice because penetrations can increase moisture risk and external walls are often load-bearing.

• Mount high enough that airflow is not obstructed by furniture (typically 2-2.3m above floor)
• Direct airflow toward the main living area, not at walls or corners
• Avoid placing directly above seating areas where direct airflow causes discomfort
• Ensure adequate clearance above and around the unit for maintenance access
• Consider sight lines; you will see this unit every day

The Outdoor Unit Matters Too

Every high wall heat pump has an outdoor unit that extracts heat from outside air (in heating mode) or expels heat (in cooling mode). Outdoor unit placement affects performance and neighbourhood relations more than many homeowners realise.

Outdoor units need adequate airflow and should not be crammed into tight spaces or surrounded by plants. They also produce noise, particularly on high output; placing them under bedroom windows, your own or neighbours', creates problems. Prioritise manufacturer clearances, unobstructed airflow, maintenance access and compliance with local noise rules; ask the installer to assess site exposure.

Understanding Efficiency Ratings

Heat pump efficiency is expressed through several ratings. The most useful for New Zealand conditions is the Coefficient of Performance (COP) for heating and the Energy Efficiency Ratio (EER) for cooling. A COP of 4.0 means the heat pump produces 4kW of heat for every 1kW of electricity consumed.

These ratings are measured under standard test conditions that may not reflect real-world performance in your climate. Look for energy label star ratings, which provide a simpler comparison. More stars mean lower running costs, and the difference between models is significant.

Energy labels help compare models under standardised conditions, but actual electricity use, savings and payback depend on climate, sizing, installation, settings, occupancy, electricity prices and the home.

Installation Costs and What to Expect

EECA currently gives around $4,400 as an indicative purchase-and-installation cost; obtain itemised quotes because the final price depends on the system and site. This includes the indoor and outdoor units, mounting brackets, interconnecting pipework, electrical connections, and commissioning. Premium brands and higher-capacity units cost more; budget options exist but often compromise on efficiency, noise levels, or longevity.

Installation complexity affects price. Back-to-back installations where indoor and outdoor units are on opposite sides of the same wall are simplest and cheapest. Longer pipe runs, difficult access, or multiple-storey installations increase costs. Multi-room ducted systems or multi-split configurations that run multiple indoor units from one outdoor unit cost significantly more but can be more cost-effective than separate systems for heating an entire home.

Operating Your Heat Pump Efficiently

Even the best-sized and placed heat pump will disappoint if operated poorly. The most common mistake is treating a heat pump like an old plug-in heater, turning it on when you arrive home and running it flat out until the room warms up.

EECA recommends using a timer to warm the room shortly before you wake or arrive home, and says running a heat pump continuously uses more energy overall. Setting a moderate temperature (18-21 degrees C for most situations) and letting the unit maintain it costs less than running at high temperatures or constantly adjusting settings.

Heating mode uses significantly more energy than fan mode. If your home reaches a comfortable temperature, the unit will naturally use less energy maintaining it. Use the timer and controls for the way the room is occupied; EECA recommends switching off when heating is not needed.

Maintenance Matters

Clean filters are essential for efficient operation. EECA recommends cleaning removable filters about once a month during winter, and more frequently if particularly dirty. Clogged filters restrict airflow, forcing the unit to work harder for less output. Cleaning takes minutes and costs nothing.

Follow the manufacturer and installer’s maintenance and servicing instructions, including any specific warranty conditions. The outdoor unit should be kept clear of debris, leaves, and vegetation that could restrict airflow.