Quick answer: Not very. A modern air source heat pump runs at a soft hum — broadly comparable to a fridge or quiet conversation, around 40–60 dB at the unit — and fades into the background a few metres away. Noise rules protect your neighbours, and careful siting is the biggest factor in what you’ll actually hear.
Noise is one of those worries that grows in the imagination. People picture a jet engine bolted to the house. The reality is far quieter — but it’s a fair question that deserves a proper answer.
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How Loud Is an Air Source Heat Pump in Decibels?
A heat pump running normally sits around 40–60 dB at the outdoor unit — a soft hum or gentle whir, audible up close but fading indoors or a few metres away.
| Sound | Approx. level | How it feels |
|---|---|---|
| Whisper / quiet library | ~30 dB | Barely audible |
| Air source heat pump (at unit) | ~40–60 dB | Soft hum |
| Fridge / quiet conversation | ~40–50 dB | Background |
| Normal conversation | ~60 dB | Clearly present |
| Washing machine | ~70 dB | Noticeable |
| Lawnmower / traffic | ~80–90 dB | Loud |
Levels are indicative and vary by model, distance and siting.
It is not a machine that dominates a garden or a street. The number matters less than what it feels like to live beside — and that’s: not much.
What Does a Heat Pump Actually Sound Like?
Like the low, constant ambient hum already present in most homes — closer to a fridge than to traffic or a lawnmower.
Decibels are slippery because the scale isn’t linear, so raw figures don’t tell you much alone. Comparison helps: the steady sound of a heat pump is worlds away from a mower or a full-volume conversation, and much closer to the background hum your ear stops registering after a minute. Where you might notice it is on a still night with no wind or traffic — even then it’s a gentle presence, and sensible siting keeps it away from bedroom windows.
Are There Noise Rules to Protect Neighbours?
Yes — a formal noise requirement is assessed at your neighbour’s property, not yours, so the installation is designed to protect the people next door from the start.
That’s a reassuring bit of engineering: the protection points outward. Meeting it shapes where the unit can go and, in tighter spots, which model makes sense. It’s not a hoop to jump through — it’s a guarantee the finished install sits comfortably in a residential street.
What Affects How Much Noise You’ll Hear?
Mostly installation, not the appliance — siting, mounting and model choice make the biggest difference.
- Siting — a unit tucked away from windows and reflective corners is quieter than the identical unit crammed into a spot that bounces sound around
- Mounting — a solid, well-considered fixing avoids the rattles and vibrations that turn a quiet machine noisy
- Model — some units are engineered to run notably quieter than others
The through-line: noise is largely designed in or out at installation. A quiet heat pump installed carelessly becomes noisy; a careful install makes even a busy unit unobtrusive.
What Are the Quietest Air Source Heat Pumps?
Several models are specifically engineered for low-noise running — worth choosing if you have a tight garden, a nearby bedroom window or a close boundary.
We factor this in routinely for the closely-packed terraced and tenement homes around Edinburgh, where boundaries are near and gardens are small. It’s exactly the sort of Scottish-street reality a good survey accounts for.
Why Siting Matters More on Scottish Streets
Because much of Scotland’s housing is terraced and tenement — homes shoulder to shoulder with a boundary just metres away — placement matters far more than in a detached home with a big garden.
The difference between a well-placed unit and a thoughtless one is far more noticeable when your neighbour’s wall is right there. The flip side: we do this constantly, so we know how to place a unit in a tight Scottish plot and keep it quiet, compliant and out of everyone’s way.
The Bottom Line on Heat Pump Noise
Air source heat pumps are far quieter than most people fear, the rules actively protect the people around you, and the biggest single factor in what you’ll notice is a careful, well-planned installation.
If a nearby boundary or window is on your mind, our free survey includes a noise siting check — so we can position your unit to keep it quiet from day one.
