Are Air Source Heat Pumps Noisy? What UK Homeowners Need to Know
Modern air source heat pumps are generally not excessively noisy when they are correctly selected, positioned and installed. The outdoor unit does make a noticeable sound while operating because it contains a large fan and compressor, but a properly designed installation should take noise into account before the heat pump is fitted.
If you are considering an air source heat pump in Horley, Reigate, Redhill, Crawley, Surrey or West Sussex, it is understandable to wonder what it will sound like outside your home and whether your neighbours will hear it. In this guide, we will explain:
- What an air source heat pump actually sounds like
- Why heat pumps make noise
- How loud modern heat pumps are
- Whether you can hear a heat pump inside the house
- Why the location of the outdoor unit matters
- How neighbours are considered
- What MCS 020a means for heat-pump noise
- Whether heat pumps become louder in cold weather
- What unusual noises can mean
- How a professional installation can minimise noise
What does an air source heat pump sound like?
An air source heat pump normally produces a steady mechanical airflow sound while it is operating. The easiest comparison is the sound of a large fan running outside rather than the firing, combustion or exhaust noise associated with some traditional heating equipment.
The exact sound varies between heat-pump models and operating conditions.
Standing immediately beside an outdoor unit will naturally make it sound more noticeable. Move further away, go behind a suitable barrier or go inside the property and the perceived sound can be significantly different.
This is why simply looking at a manufacturer’s headline noise figure does not tell you exactly what a particular installation will sound like at your neighbour’s window or inside your bedroom.
Why does an air source heat pump make noise?
An air source heat pump contains moving mechanical components. The main sources of sound are normally the fan and compressor.
The fan moves outside air through the outdoor unit so the system can collect heat from it. The compressor is part of the refrigeration circuit that allows that captured heat to be transferred into your heating and hot-water system.
These components operate at different speeds depending on how much heat the property requires.
Modern inverter-controlled heat pumps can adjust their output rather than simply operating at maximum power every time they switch on. This helps the system respond to changing heating demand, although the actual operating behaviour depends on the equipment and system design.
How loud is a modern air source heat pump?
There is no single noise level that applies to every air source heat pump.
Different models have different sound characteristics, and there is also an important difference between sound power and sound pressure.
Sound power describes the acoustic energy produced by the equipment itself. Sound pressure describes the sound experienced at a particular position and is affected by factors such as distance, walls and other barriers.
This distinction matters when comparing heat pumps. A manufacturer’s sound-power figure should not simply be treated as the noise level somebody will experience several metres away.
A professional installer should use the appropriate manufacturer’s acoustic information when assessing the proposed installation.
Can you hear a heat pump from inside your house?
You may be able to hear an outdoor heat pump from inside in some circumstances, but a properly designed installation should consider this before the equipment is positioned.
How noticeable it is indoors can depend on:
- how close the outdoor unit is to windows and doors
- the construction of the external wall
- whether the unit is close to a bedroom
- how the equipment is mounted
- vibration isolation
- the particular heat-pump model
- how hard the system is operating
For example, putting an outdoor unit immediately beside a bedroom window deserves much more careful consideration than positioning it appropriately away from sensitive rooms.
There is no universal “perfect” position because every property is different.
Does the position of a heat pump affect how noisy it is?
Yes. Positioning is one of the most important parts of managing heat-pump noise.
The installer needs to consider not only where the unit physically fits, but how sound may travel from that location.
A heat pump positioned in a confined area between reflective walls can behave differently acoustically from one installed in a more open location. Nearby walls, corners and barriers can therefore matter.
The location must also provide the clearances and airflow required by the heat-pump manufacturer. Trying to hide a heat pump in an unsuitable enclosure simply to reduce noise can restrict airflow and affect operation.
At JPEC Green Energy, outdoor-unit location forms part of the system-design process rather than being decided after the rest of the installation has already been planned.
Will my neighbours hear my heat pump?
Possibly, but that does not mean the heat pump will create an unreasonable disturbance.
Distance between the heat pump and nearby properties matters because sound reduces as you move away from its source. The direction and position of surrounding walls and barriers can also affect the sound reaching a neighbouring property.
This is particularly important for homes with smaller gardens or properties that are close together, which are common in parts of Horley, Redhill, Reigate and Crawley.
Rather than guessing whether a neighbour will hear the unit, the proposed location should be assessed properly during the design stage.
This can sometimes mean choosing a different position or reconsidering the equipment selection before installation begins.
What is the MCS 020a heat-pump noise assessment?
MCS 020a is the planning standard currently used to assess noise from air source heat pumps where an installation is relying on permitted development rights in England.
Permitted development means certain work can be carried out without making a full planning application, provided all of the relevant limits and conditions are satisfied.
The MCS 020a assessment considers factors including:
- the manufacturer’s sound-power data
- the position of the heat pump
- the distance to the relevant assessment position
- how the unit is positioned in relation to surrounding surfaces
- the effect of qualifying barriers
- the calculated sound pressure at the assessment position
Under the current MCS 020a methodology, the calculated sound pressure at all relevant assessment positions must be no higher than 37.0 dB(A) to meet the permitted-development noise limit.
This does not mean every heat pump itself has to be rated at 37 dB(A). The calculation is about the predicted sound level at the relevant assessment position, not simply the manufacturer’s headline sound figure for the outdoor unit.
Do air source heat pumps need planning permission because of noise?
Not necessarily. In England, an air source heat pump installed at a domestic property can often fall under permitted development, meaning a full planning application is not required, provided all of the applicable conditions and limitations are met.
Noise is one of those considerations.
From 28 May 2026, Planning Portal guidance states that MCS 020a is the permitted certification scheme used for this aspect of domestic air source heat-pump permitted development.
There are other conditions as well, so passing the noise assessment does not by itself guarantee that an installation is permitted development.
Different rules can apply to listed buildings, conservation areas, flats, commercial properties and other particular circumstances. Permitted-development rights can also be restricted locally.
If there is any doubt, the planning position should be checked before installation rather than assumed.
Are heat pumps louder when it is cold outside?
A heat pump’s sound can change depending on operating conditions.
When the weather becomes colder, your home generally requires more heat. The heat pump may therefore need to work harder than it does during milder conditions.
Fan and compressor speeds can change as the unit adjusts its output, so the sound may not remain identical throughout the day or throughout the year.
This is another reason why choosing the correct size matters. The aim is not simply to buy the biggest unit available, but to select equipment capable of meeting the property’s calculated heating demand at the required design conditions.
A proper heat-loss calculation should form part of that process.
Why does a heat pump sometimes make a different noise in winter?
During cold and damp weather, frost can form on the outdoor heat exchanger. The heat pump therefore periodically needs to remove this frost using a process called a defrost cycle.
During defrost, you may notice the fan change or stop temporarily, the operating sound change and water appear beneath or around the outdoor unit.
You may also occasionally see what looks like steam or vapour around the unit as the frost clears.
These things can be part of normal heat-pump operation and do not automatically indicate a fault.
However, drainage around the outdoor unit should be designed correctly so that condensate and defrost water can be managed appropriately, particularly during freezing conditions.
What heat-pump noises should you get checked?
A steady fan and compressor sound is expected. A sudden or significant change from the way the system normally operates deserves more attention.
You should consider having the system checked if you notice persistent unusual sounds such as excessive rattling, grinding, severe vibration or another noise that has appeared unexpectedly.
The cause could be relatively straightforward, but it is better to have the equipment assessed than attempt to dismantle or modify the outdoor unit yourself.
A heat pump contains electrical components and a sealed refrigerant circuit, so internal repairs and refrigeration work are jobs for appropriately qualified professionals.
Can heat-pump noise be reduced after installation?
Sometimes, but prevention is better than trying to correct a poorly chosen location afterwards.
Depending on the cause, possible professional solutions might involve checking mounting arrangements, vibration isolation, system settings or whether something has become loose or damaged.
Moving an outdoor unit is a much more significant job because refrigerant or water connections, electrical supplies, drainage and the wider system design may all be affected.
Acoustic barriers can be appropriate in some situations, but they must be designed without preventing the airflow and servicing access required by the manufacturer.
You should not box in or obstruct a heat pump in an attempt to make it quieter.
How should a quiet heat-pump installation be designed?
A good installation starts before the outdoor unit arrives at your property.
The installer should assess the building, calculate the required heating output, choose appropriate equipment and determine a sensible outdoor location.
Noise should be considered alongside:
- heat-pump performance
- manufacturer clearances
- airflow
- neighbouring properties
- windows and sensitive rooms
- service and maintenance access
- pipework routes
- condensate drainage
- electrical requirements
- planning and MCS requirements
For a home in Crawley with a narrow side passage, the best solution may therefore be different from a detached property outside Reigate with a large garden.
It is the complete installation that matters, not simply choosing a heat pump advertised as quiet.
Should heat-pump noise put you off installing one?
For most suitable properties, noise alone should not automatically put you off an air source heat pump.
UK government research into air source heat-pump noise found that noise was a concern for a minority of consumers in the study and that reported complaints were relatively uncommon. Where complaints did arise, poor installation quality, location and proximity were identified as important factors.
That does not mean noise should be ignored. It means it should be properly designed for.
Before agreeing to an installation, you should understand where the outdoor unit will be positioned, why that position has been selected and whether the required noise and planning assessments have been completed.
JPEC Green Energy can help
If you are considering an air source heat pump, JPEC Green Energy can survey your property and design the system around the building rather than simply choosing somewhere convenient to place the outdoor unit.
Our heat-pump design process can consider heat loss, equipment sizing, radiator requirements, hot-water demand, outdoor-unit location, noise, electrical requirements and the relevant MCS and planning considerations.
JPEC Green Energy installs Mitsubishi Ecodan air source heat pumps for suitable properties across Horley, Reigate, Redhill, Crawley, Surrey and West Sussex.
We can explain the proposed outdoor-unit position, what you can expect from the system and any limitations or requirements identified during the survey.
To arrange a survey, discuss your property and receive a properly designed quotation, contact JPEC Green Energy.
This article provides general information and is not personal planning, legal or technical advice. Heat-pump suitability, noise performance, permitted-development status and installation requirements depend on the individual property, equipment and proposed location and should be confirmed through an appropriate survey and system design.
