At night you hear two things: the indoor fan in the room, and the outdoor unit through the wall or the window. Choose a low fan speed, use the night setting if the model has one, and put the condenser on a heavy wall away from bedrooms, yours and the neighbour's. A published decibel figure is for a stated test, not a promise at your fence with the window open. Survey that position first. F-gas commissioning should leave the system able to tick over, not hunt. Planning noise calculations are a different test from what you hear at one in the morning.
The fan by the pillow and the compressor outside
The indoor unit on its lowest speed is what bedroom shoppers compare. Mitsubishi AY is popular for that reason. Mitsubishi Electric publishes those low-speed figures. Other brands can be fine when their own sheet, for that kW, is actually quiet. High fan, boost and a swing vane aimed at the pillow are choices, and they are loud choices.
The outdoor unit is the one that wakes the neighbour and, if it is on the same wall, wakes you. Anti-vibration mounts, solid masonry rather than a fence panel, and clear airflow so the fan is not fighting a blockage all help. A night mode does not move a bad bracket.
A modest setpoint and a sleep mode
A modest setpoint beats a very low one that forces the unit to run hard all night. Timers can pre-cool the room and then ease off. Sleep modes usually raise the setpoint slightly and drop the fan. They are worth using. They are not a substitute for capacity. An undersized unit will stay loud because it never catches up.
Read sound data at the lowest fan speed for your exact size. Keep condensers off bedroom windows. Isolate the outdoor unit. Do not box it in. A hunting compressor is a fault, not a feature. GOV.UK F-gas commissioning should leave the system able to tick over. If night heating is part of the job, say so when the outdoor position is chosen.
An open window, a party wall, and a calculation that is not 1am
An open window invites outdoor noise in. A shut window and a running split is the point of the install, with enough fresh air at other times of the day. Party walls transmit vibration even when the window is shut. Fixings and isolation matter more there than the indoor fascia.
In England, the Planning Portal summary of Class G permitted development points at the MCS 020a noise standard and still requires that the unit is not used solely for cooling. Meeting it is not a guarantee nobody hears the unit. GOV.UK explains how councils deal with noise complaints if a neighbour says the unit is a nuisance. Failing siting common sense will annoy someone even if a form was signed. Say the room is for sleep, name the neighbour's bedroom if it is close, and ask for the outdoor sound data and the mounting method. Compare like-for-like kW. A photo of the bedroom wall and the outside at the head of the bed lets the installer mark a position that is not under a window. Commissioning should include the quiet setting you will actually leave on.
Frequently asked questions
Which is louder at night, the indoor or the outdoor unit?
In the bed, usually the indoor fan if the outdoor unit is well placed. For the neighbour, almost always the outdoor unit. Treat both. A quiet fascia on a noisy bracket still fails.
Will night mode make any unit suitable for a bedroom?
No. It trims fan and setpoint on a unit that was already reasonable. It will not silence a condenser outside the window or an undersized system running flat out.
Is the planning noise calculation what I will hear?
It is a compliance method for permitted development, not a recording of your window at 1am. Use it for the legal check, and use siting and sound data for sleep.
Does winter defrost belong under a bedroom window?
Defrost makes a reverse-cycle outdoor unit pause and restart. That is normal, and it is a reason not to stand the unit under a light bedroom window if you will heat overnight.
Will a quieter badge at the wrong size stay quiet?
No. An undersized unit stays loud because it never catches up. Compare like-for-like kW, and read sound data at the lowest fan speed for that size.
Core buying guides
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How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.