Noise is the second question we get asked, usually straight after price, and usually by someone thinking about a bedroom. It is a fair question, and the answers online are useless, because they either quote a decibel figure with no context or they promise you silence. Here is what a modern system actually sounds like in a real house, and what decides it.
In this guide
The short answer
A modern, properly installed system on a low fan speed is quiet enough that most people stop noticing it within a day. It is not silent. Nothing that moves air is silent.
The sound it makes is a soft, steady rush of air with a faint hum behind it. Because it is constant and has no pattern, your ear files it away with the fridge and the boiler. Almost nobody rings us about the noise of a system that is working properly. The complaints we get are about systems that were sited badly or are running flat out because they are too small for the room.
What the decibel figure is telling you
Every manufacturer publishes sound figures for every model, at each fan speed, and they are worth reading. Two things about them are worth understanding first.
The decibel scale is logarithmic rather than linear. That means the gap between two figures is a bigger real difference than the numbers suggest. A few points on paper is a change you will hear, not a rounding error. It is why comparing two models on their quoted figures is genuinely useful, even though the figure itself will not tell you what your room will sound like.
The other thing is that a single quoted figure usually refers to the lowest fan speed. That is the honest best case. The same unit on maximum, pulling a hot room down on the first afternoon of a heatwave, is a different and noticeably louder machine.
Why the brochure number is not what you hear
Published sound figures are measured under controlled test conditions at a stated distance. Your bedroom is not a test chamber. Hard floors, bare walls and big windows bounce sound around, and a room full of carpet, curtains and a wardrobe absorbs it.
So treat the figures as a fair way to compare one model against another, and a poor way to predict a room. Two identical units in two Teesside bedrooms will not sound the same, and neither of them will sound like the lab.
What the indoor unit sounds like
The indoor unit is a fan and a coil. Nearly all the sound is moving air, which is why fan speed matters more than anything else you can control.
- Low or quiet mode. A soft rush. Most people find this comfortable to sleep through, and most units have a night or quiet setting that trades a little speed for a lot of calm.
- Medium. Clearly audible, entirely unremarkable. Fine for a lounge with the television on.
- High. Noticeable. You would not choose it in a bedroom, and you rarely need it once a room is at temperature.
- Occasional clicks and gurgles. Refrigerant moving and condensate draining. Normal, and quieter on better units.
This is where inverters changed the conversation. An older non-inverter system ran flat out or not at all, so you got a loud machine, silence, then a loud machine again. That switching is far more intrusive than a constant sound. An inverter throttles back once the room is there and holds it, which usually means it settles to a low, steady murmur and stays there. Our guide on inverter and non-inverter systems goes into why.
The outdoor unit and your neighbours
The outdoor unit is the noisier half, because it holds the compressor and a bigger fan. It is also the half that is nowhere near your ears and, in most Teesside houses, further from your neighbours than people fear.
Realistically, standing next to it you will hear a hum and a fan. From inside your house with the window shut, most people cannot hear it at all. The people worth thinking about are next door, particularly in the terraced and semi detached streets around Middlesbrough, Thornaby and Norton where yards are small and walls are close.
This is not just courtesy. Air conditioning normally falls under permitted development for a home in England, but that permission comes with conditions, and they cover siting and noise. Listed buildings and conservation areas are treated differently again. We check all of this at survey rather than leaving you to find out afterwards, and our guide on planning permission covers it in more detail.
Siting changes everything
If you take one thing from this article, take this. Where the outdoor unit goes does more for noise than which model you buy.
- Distance is free. Sound falls away quickly with distance. A few extra metres of pipe run is usually cheaper than a problem you cannot fix later.
- Do not point it at a bedroom window. Yours or theirs. Obvious, and still the most common mistake we are called out to correct.
- Mind the corners. A unit tucked into a tight corner between two hard walls reflects its own sound back and outwards. An open aspect is quieter and works better.
- Mount it properly. Vibration through a wall is the complaint people actually make. Good brackets, anti-vibration mounts and a solid fixing matter more than the badge.
- Do not box it in. Enclosing a unit to hide the sound starves it of air, which makes it work harder, which makes it louder. It is the one fix that reliably backfires.
What actually makes a system noisy
When a system is genuinely too loud, it is almost never because the unit was a noisy model. It is one of these.
- It is undersized. A unit too small for the room never reaches the set temperature, so it never throttles back. You have bought a machine that runs at full fan all day. This is the big one.
- It was mounted on the cheap. Vibration into a wall or a joist turns a quiet compressor into a sound the whole house shares.
- It is dirty. Choked filters and coils make the fans fight for air.
- It is boxed in or blocked. Same problem, outside.
- It is old and non-inverter. The hard on and off cycling is what people remember, and what they expect from anything new.
Notice that four of those five are installation and maintenance rather than equipment. That is the honest heart of this. A well sized, well mounted mid range system is quieter in your house than a premium unit fitted badly.
Noises that mean something is wrong
A soft rush of air and a low hum are the system working. These are not.
- Grinding or screeching from either unit, which usually means a bearing or a fan
- A rattle that has appeared recently, often a loose panel or a bracket working itself free
- Buzzing that comes with a smell, which means switch it off and ring someone
- A new hard clunk each time it starts or stops
New noises are worth acting on early. Nearly all of them are small and cheap when caught, and the same faults ignored until August are the ones that end in a compressor.
Getting an honest answer for your room
We will not promise you silence, because we would be lying and you would find out. What we will do at survey is talk about where the units can go, what you will hear at night, and what your neighbours will hear, before anything is ordered.
We are a family run business on North Ormsby Road in Middlesbrough, covering roughly twenty miles of Teesside: Stockton on Tees, Thornaby, Billingham, Norton, Yarm, Eaglescliffe, Ingleby Barwick, Redcar, Marske, Saltburn, Guisborough, Marton, Hartlepool, Peterlee and Darlington. The survey is free and there is no obligation. Ring us on 01642 680 873.
