Heat Pump Noise: How Loud Are They Really?
A typical air source heat pump runs at 42 to 50 dB measured at 1 metre, dropping to 35 to 42 dB at 3 metres. For context, that is quieter than a normal conversation (60 dB) and similar to a modern refrigerator. The permitted development noise limit is 42 dB at the nearest neighbour's window. Most correctly installed units meet this comfortably. This guide covers real-world noise levels, planning rules, how to reduce noise, and what to do if neighbours are concerned.
How loud is 42 dB?
Decibels are not intuitive. Here is how heat pump noise compares to everyday sounds you already know.
| Sound | Level (dB) |
|---|---|
| Quiet library | 30 |
| Modern refrigerator | 35 to 40 |
| Heat pump at 3 metres | 35 to 42 |
| Quiet office | 40 to 45 |
| Heat pump at 1 metre | 42 to 50 |
| Normal conversation | 55 to 65 |
| Gas boiler (external flue) | 45 to 60 |
| Lawnmower | 85 to 90 |
Decibels use a logarithmic scale. Every 10 dB increase sounds roughly twice as loud. A 50 dB heat pump sounds about half as loud as a 60 dB conversation.
Importantly, the sound a heat pump produces is a continuous low hum, not a sharp or intermittent noise. Most homeowners report that they stop noticing it within days. It is very different from the stop-start clatter of an old gas boiler or the rattle of an air conditioning unit.
Planning rules on noise
In England, air source heat pumps can be installed under permitted development without planning permission if they meet several conditions. The noise condition is the one most people worry about.
The 42 dB limit: The heat pump must not exceed 42 dB(A) when measured 1 metre from the nearest neighbouring property's habitable room window. This is a condition of permitted development, not a standalone regulation. If the unit would exceed 42 dB at that measurement point, you need full planning permission.
How distance helps: Sound drops by approximately 6 dB each time you double the distance from the source. A unit producing 48 dB at 1 metre will produce roughly 42 dB at 2 metres, 36 dB at 4 metres, and 30 dB at 8 metres. For most semi-detached and detached homes, placing the unit 3 to 5 metres from the boundary is enough to meet the limit.
Terraced houses: Properties with short gardens or shared boundaries need more careful placement. A unit against a party wall or within 2 metres of a neighbour's window may exceed the limit. Your MCS installer should calculate the expected noise level at the boundary as part of the design. Read our planning permission guide for the full rules.
Ask your installer for a noise assessment
Any competent MCS installer will calculate the noise level at your nearest neighbour's window before installation. If the result is borderline, they can recommend quieter units, better placement, or acoustic measures. This assessment should be included in your quote at no extra cost.
What affects noise levels
Unit size and model
Larger heat pumps (12+ kW) tend to be louder than smaller ones (6 to 8 kW) because they have bigger compressors and fans. However, modern premium units from manufacturers like Vaillant, Daikin, and Samsung have invested heavily in noise reduction. Some 10 kW units now run at 40 dB at 1 metre, quieter than many 6 kW units from five years ago.
When comparing quotes, ask each installer for the sound power level (dB(A)) of the specific model they propose. This is stated in the product datasheet and allows direct comparison.
Operating mode
Heat pumps are loudest when working hardest: during the coldest weather and during defrost cycles. On a mild spring day, the unit may run at 38 dB. On a cold January night when demand is highest, it may reach 48 to 50 dB. The defrost cycle (a brief burst every 30 to 90 minutes in cold weather) produces a slightly different sound as the system reverses to melt ice from the outdoor coil. This is normal and lasts 2 to 5 minutes.
Placement
Where you put the outdoor unit significantly affects perceived noise. Hard walls, corners, and enclosed spaces reflect and amplify sound. An open position away from walls and boundaries is best. Avoid placing the unit directly below bedroom windows (yours or your neighbour's), in narrow side passages between houses, or in enclosed courtyards.
Vibration
A heat pump bolted directly to a concrete plinth can transmit vibration into the ground and through building structures, creating a low-frequency hum indoors that is separate from airborne noise. This is easily prevented with anti-vibration mounts. See recommended anti-vibration pads that sit between the unit and the plinth.
How to reduce heat pump noise
Choose a quiet unit. Specify noise as a selection criterion when getting quotes. The quietest air source heat pumps on the UK market now achieve 38 to 42 dB at 1 metre. Paying slightly more for a quieter model is worth it, especially on terraced properties.
Maximise distance. Every extra metre between the unit and your neighbour's window helps. If you can place the unit at the far end of your garden rather than against the house, do so (though this increases refrigerant pipe runs and may add cost).
Use anti-vibration mounts. Rubber or spring mounts between the heat pump and its plinth prevent vibration transfer into the ground. This eliminates the low-frequency hum that travels through structures. See recommended anti-vibration pads. These cost £30 to £80 and make a noticeable difference.
Avoid reflective surfaces. Do not box the unit in with walls or fences on three sides. Sound bounces off hard surfaces and amplifies. If you need screening for appearance, use acoustic fencing with sound-absorbing material on the inner face, or plant dense hedging at least 1 metre from the unit to allow airflow.
Consider an acoustic enclosure. Purpose-built acoustic enclosures reduce noise by 5 to 10 dB while maintaining airflow. They cost £500 to £1,500 and are worth considering for installations close to boundaries. They must not restrict airflow to the unit, as this reduces efficiency.
Maintain the unit. A well-maintained heat pump runs quieter than a neglected one. Loose panels, worn fan bearings, and debris around the unit all increase noise. An annual visual check and clearing of leaves or obstructions helps.
Use night setback. Most heat pumps can reduce output overnight, which reduces noise during the hours when it matters most. See recommended smart thermostats with scheduling features that optimise comfort and noise management.
Do not restrict airflow to reduce noise
The outdoor unit needs clear airflow around it to work efficiently. Enclosing it too tightly, packing material around the fan, or blocking the air discharge reduces performance and increases running costs. Any noise reduction measure must maintain the manufacturer's minimum clearance distances.
Neighbour concerns
Even when your heat pump meets all planning conditions, a conversation with your neighbours before installation prevents problems later. Most people are reasonable when they understand what to expect.
Before installation: Let your immediate neighbours know you are installing a heat pump, where the outdoor unit will be placed, and what it will sound like. Showing them the expected noise level (37 to 42 dB at their window, equivalent to a fridge humming) is usually reassuring.
If a neighbour complains: First check that the unit is functioning correctly and that nothing has come loose or degraded. Check for vibration transfer through the plinth. If the noise level is within specification, the complaint may be addressed by adding anti-vibration mounts, adjusting the unit's night mode settings, or adding screening. If you cannot resolve it informally, the council can be asked to assess whether a statutory nuisance exists.
Statutory nuisance: Neighbours can complain to the council under the Environmental Protection Act regardless of whether the unit meets planning conditions. The council assesses whether the noise constitutes a nuisance in context. In practice, modern heat pumps meeting the 42 dB limit and correctly installed rarely result in nuisance findings.
Indoor noise
The outdoor unit is the main noise source, but the indoor system also produces some sound. The hot water cylinder may make a slight humming when the heat pump charges it. Radiators may produce a gentle ticking as they expand and contract with the lower flow temperatures a heat pump uses. Underfloor heating is virtually silent.
None of these indoor sounds are louder than a typical gas central heating system. Most homeowners find a heat pump quieter overall than their old boiler, because there is no ignition noise, no flame roar, and no rapid cycling on and off.
Noise and heat pump efficiency
There is a connection between noise and efficiency. A heat pump running at low output (partial load) is both quieter and more efficient than one running at full capacity. Well-insulated homes allow the heat pump to cruise at partial load most of the time, keeping noise and running costs low. This is another reason to insulate your home before or alongside a heat pump installation.
Read our running costs guide for how insulation and tariff choice affect your bills. Use our heat pump calculator for a cost estimate that accounts for your insulation level.
Frequently asked questions
How loud is a heat pump?
42 to 50 dB at 1 metre, 35 to 42 dB at 3 metres. Similar to a fridge, quieter than a conversation. See our cost by house type guide for sizing that affects noise output.
What is the planning noise limit for heat pumps?
42 dB(A) measured 1 metre from the nearest neighbour's habitable room window. Read our planning permission guide for all permitted development conditions.
Can neighbours complain about heat pump noise?
Yes, via a statutory nuisance complaint. In practice, modern units meeting the 42 dB limit rarely result in findings. Good placement and anti-vibration mounts prevent most issues.
How can I make my heat pump quieter?
Anti-vibration mounts (see recommended pads), maximise distance from boundaries, avoid enclosed corners, consider an acoustic enclosure for sensitive locations, and maintain the unit annually.
Are heat pumps noisier in cold weather?
Slightly. They work harder and run defrost cycles. This adds 2 to 5 dB over mild-weather baseline. Better insulation reduces the load and keeps the unit quieter.
Data sources
Planning rules from GOV.UK permitted development guidance. Noise levels from manufacturer product datasheets and Energy Saving Trust.