Noise is usually manageable with the right model and placement. Judge the calculated sound at relevant neighbouring windows, not a single manufacturer decibel figure.
What will you hear?
An outdoor unit has a fan and compressor, so it makes a steady mechanical sound while running. It can be more noticeable during high demand or a defrost cycle. The sound at your bedroom or a neighbour's window can be very different from the manufacturer's test figure because distance, walls and reflections change it.
In a 2026 government follow-up of Boiler Upgrade Scheme recipients, 89% of respondents were satisfied with their system's noise level. That is useful context, but it does not guarantee a particular installation will be quiet.
A planning calculation is more useful than a brochure number
For permitted development in England, MCS 020(a) sets a calculated limit of 37 dB(A) at the specified assessment position. The installer should carry out this assessment for your proposed model and location. It accounts for where the unit sits in relation to the assessed neighbouring property.
A unit tucked into a hard-walled corner may reflect sound differently from one with open space around it. Ask for the site plan and completed assessment, then discuss any bedroom windows or outdoor seating areas that matter to your household.
Questions that prevent a bad surprise
Ask where the unit will sit, which direction its fan faces and whether the quoted model has a lower-noise mode. Check that any acoustic enclosure will preserve airflow and service access. A heat pump should never be boxed in simply to hide it.
If two installers propose very different positions, ask each to explain the trade-off between noise, pipe length, visual impact and maintenance access. Get the agreed position into the final design.
If the installed unit seems louder than expected
First check that the outdoor unit is clear of leaves, stored items and anything touching the casing. Note whether the sound occurs during normal heating, hot-water production or a short defrost cycle. Send that detail to the installer and ask them to inspect the unit and compare its operation with the commissioned design.
A planning sound assessment describes a predicted level at a specified position. It does not replace a proper investigation if the real installation creates a problem. Keep the original calculation and model specification so the installer can see what was promised.
A note about the numbers
Prices, grants and tariffs can change. The dated figures above come from the linked sources and are examples unless explicitly described as a published average. Your installer should assess your property before giving a final design or quotation.