Heat pumps are not silent, but modern systems are typically quiet enough that, when correctly selected and installed, they fade into background noise for most households. The important detail is where the sound comes from, how it is measured, and how quickly it drops off with distance.
Where the noise comes from
Outdoor unit
The outdoor unit is the main source of heat pump noise. It contains a fan and a compressor, and both contribute to a steady “hum” and airflow sound. Noise can increase during high load conditions (very cold or very hot weather) and during defrost cycles on heating.
Indoor unit
Indoor units mainly produce fan noise as air moves through the unit. At low fan speeds, this is often comparable to quiet background sound. Higher fan speeds are more noticeable, especially in bedrooms and small rooms.
Understanding decibels and why numbers can be confusing
Heat pump noise is usually stated in dB(A) (A-weighted decibels), which approximates how humans perceive sound.
Two measurements matter:
- Sound pressure level: what you hear at a specific distance (often quoted at 1 metre).
- Sound power level: the total sound energy emitted by the unit, measured using a standardised method and useful for comparing models.
Sound pressure depends heavily on installation conditions and distance, so two identical units can “sound” different in real life even if their sound power is the same.
Typical heat pump noise levels
Exact figures vary by brand, capacity, and operating mode, but modern residential systems commonly fall into these ranges:
- Outdoor unit: often around 40–60 dB(A) at 1 metre, depending on load and model.
- Indoor unit: typically quieter than the outdoor unit at low fan speeds, and more noticeable at higher airflow settings.
What matters most is what the sound is like at the boundary and at bedrooms, not what it is at 1 metre from the unit.
How quickly noise drops with distance
Sound reduces as you move away from the source. In practical terms, the noise at a boundary several metres away can be substantially lower than the “at 1 metre” figure, especially if the unit is not facing reflective surfaces and is mounted to minimise vibration.
This is why placement and mounting often matter as much as the model choice.
Noise compliance and neighbour considerations in New Zealand
Heat pump noise issues in New Zealand are usually managed through:
- the Resource Management Act, which places a duty on occupiers of land to avoid unreasonable noise and adopt the best practicable option to keep noise at a reasonable level
- district plan rules and council noise control processes, which can apply specific limits or assessment methods in residential areas
- recognised measurement and assessment methods such as NZS 6801 (measurement) and NZS 6802 (assessment) used across environmental noise management in New Zealand
Councils commonly receive heat pump complaints when the outdoor unit is placed close to boundaries and facing neighbouring bedrooms or living spaces.
When a heat pump will sound louder than expected
Heat pumps are more likely to be considered “noisy” when one or more of these conditions apply:
- the outdoor unit is mounted on a wall that transmits vibration into a room
- the unit faces a hard surface that reflects sound (walls, narrow side passages, courtyards)
- the unit sits on an uneven or resonant base
- the system is oversized, causing frequent ramping up and down
- the unit is forced to run at high output because of poor placement, restricted airflow, or lack of maintenance
Practical ways to reduce heat pump noise
Choose the right unit for the space
Correct sizing reduces unnecessary high-speed operation. Sound power figures and “quiet mode” functions help compare models, but installation quality still dominates real-world results.
Position the outdoor unit for low impact
Prioritise:
- distance from bedroom windows (yours and neighbours)
- avoiding direct line-of-sight to a neighbour’s most noise-sensitive rooms
- avoiding tight corners and reflective cavities that “trap” sound
Control vibration
Good mounting and isolation reduce low-frequency hum and structure-borne noise, which is often what people find most irritating indoors.
Keep the system maintained
Blocked coils, worn fan bearings, and loose panels can push noise higher than the unit’s normal operating level.
A useful benchmark for night-time noise sensitivity
If the outdoor sound level near bedrooms is high enough to disturb sleep, it will generate complaints regardless of whether it is technically compliant. WHO night noise guidance identifies 40 dB (night outside) as a target to protect public health.