How Noisy Is an Air Source Heat Pump? My Readings, Spec Sheets and UK Rules

Last updated: September 2026

How noisy is an air source heat pump? A customer asked me this a while back, and honestly it wasn’t something I’d thought much about. I’d been happily running one on my own hot tub, loving how fast it heats and what it’s done to my bills. But if you’re putting one a few metres from your own patio, or your neighbour’s bedroom window, it’s a very fair question. So I got the decibel meter out and made a video about it.

In this post I’ll share what I measured on my own Comfortline, what the manufacturer’s spec sheets say, what the UK rules on heat pump noise actually are, and how to site a heat pump so nobody (you included) gets annoyed by it.

Where the noise comes from

An air source heat pump has two noisy parts: the fan, which pulls air through the big coil on the back or side, and the compressor, which does the actual work of moving heat from the air into your water. The compressor is the main culprit. You’ll also hear the water pump that feeds it, and every so often a hiss and a whoosh as it defrosts in cold weather.

My heat pump is an inverter model, which means the compressor and fan change speed to match the heat needed. When the water’s cold, it runs flat out. As it gets close to temperature, it slows right down. That’s great for efficiency, and it matters for noise too, as you’ll see below.

What I measured on my own heat pump

I measured my Comfortline at different outputs and temperatures while it heated the tub. The readings ranged from 63dB to 71dB, with the highest reading, unsurprisingly, taken right next to the unit. So in normal use, mine sat somewhere in the 60–70dB range when I measured it.

To give you a real-world comparison, it’s similar to a split-system air conditioner. In my experience, the air con actually seems a tad louder. Sitting in the tub, it doesn’t bother me. But I wouldn’t want it blasting away right under a bedroom window.

Those numbers are higher than the spec sheets below, and it’s worth knowing why. I took them close to the unit, while it was working hard, with a handheld meter, and in a real garden with walls, fences and the tub’s own pumps running. Manufacturers measure under controlled conditions at a fixed distance. My heat pump is also the 21kW Comfortline, an earlier model than the current range. So treat my readings as “what it’s like standing next to it”, and the spec sheet as the fair way to compare one model with another.

What the spec sheets say

Here are the published figures for two current Comfortline inverter models, which is the brand I have on my own tub. The ranges run from low speed to full power.

Model	Noise at 1m	Noise at 10m	Quiet mode
Comfortline 7kW	38.8–50.2dB(A)	18.8–30.2dB(A)	Silence mode limits output to 80%
Comfortline 20kW	45.3–57.1dB(A)	25.3–37.1dB(A)	49.6dB(A) at 1m at 50% output; silence mode is about 7dB(A) quieter

Two things stand out. First, a bigger heat pump is louder at full power, because it’s moving much more air. Second, look at the gap between low speed and full power: around 11–12dB. Once your water is up to temperature, an inverter spends most of its time near the bottom of that range. That’s why the most noticeable noise is during a big heat-up from cold, not while it’s just holding temperature.

When you compare models from different makers, check the distance the figure is quoted at. A number “at 1m” and one “at 10m” for the same unit differ by 20dB. Some brands quote sound power (dB(A) L_w) instead, which is a different measure again and always a bigger number. Compare like with like.

Decibels, distance and why it matters

Decibels are logarithmic, so they don’t add up the way you’d expect. A few rules of thumb help:

• Every doubling of distance in open air knocks about 6dB off. You can see it in the Comfortline figures: from 1m to 10m, the level drops by exactly 20dB.
• Walls close to the unit make it louder. Sound bounces off hard surfaces. That’s why the MCS calculation adds to the level for each wall or surface within a metre of the heat pump. A heat pump tucked into a corner is noticeably louder than the same unit in the open.
• A solid barrier between the unit and the listener makes it quieter. The MCS 020 a) method allows up to 10dB off for a brick or masonry wall and 5dB for a solid fence, when you can’t see the heat pump from the window. Open fences and planting don’t count.
• Around 10dB higher sounds roughly twice as loud. So the difference between low speed and full power on these units is very noticeable.

UK rules on heat pump noise

In the UK, heat pump noise is judged at your neighbour’s window, not in your garden.

• The Energy Saving Trust says heat pumps typically can’t be installed without planning permission if the noise exceeds 42dB measured 1m from a neighbouring window. Many councils quote the same 42dB figure. Central Bedfordshire’s guidance, for example, uses 42dB LAeq at the boundary with any neighbouring home.
• In England, the permitted development rules changed in May 2025. MCS says installations now need to comply with MCS 020 a), and the same changes allow heat pumps within 1m of the boundary. The MCS 020 a) calculation checks that the heat pump’s sound level is 37.0dB(A) or lower at 1m from the centre of any door or window to a habitable room of a neighbouring property. The calculation works from the unit’s sound power, the distance, reflecting walls and any barrier.

An important caveat. These rules were written for heat pumps that heat homes. Whether a hot tub or pool heat pump falls under the same permitted development rules isn’t clear-cut, and it may depend on where it goes and on your council. If you’re in any doubt, particularly in a conservation area, near a listed building or close to a boundary, ask your local planning department before you fit it. Either way, the neighbour’s-window benchmark is a sensible target, and your council can still act on a noise complaint whatever the planning position.

In the USA, there’s no national equivalent. Noise is covered by local ordinances, which vary by city and county, and some homeowners’ associations have their own rules. Check locally, and follow the manufacturer’s clearances.

How to keep a heat pump quiet

• Site it thoughtfully. Keep it away from bedroom windows (yours and your neighbours’), and point the fan away from where people sit. On Edward’s holiday-let hot tub on the Isle of Skye, we moved his Comfortline away from under a bedroom window for exactly this reason.
• Keep it out of corners. Each hard surface within a metre makes it louder. But leave the clearances the manufacturer asks for, because it needs to breathe.
• Put a solid barrier between it and the neighbours, like a brick wall or a close-boarded fence, so they can’t see it from their window. Don’t box it in, though. Restricting airflow makes it work harder and louder.
• Stand it on anti-vibration feet on a level, solid base. The Energy Saving Trust says excess noise sometimes means the unit needs servicing or levelling, and that anti-vibration feet can help.
• Use the quiet or night mode if yours has one. On the Comfortline 20kW, silence mode is about 7dB(A) quieter.
• Size it sensibly. An inverter that’s big enough spends most of its time at low speed. An undersized one runs flat out for hours.
• Check it’s the heat pump. A rattling, grinding or screaming noise is often the water pump, not the heat pump. See Noisy hot tub pump?
• Keep it clean and serviced. A blocked coil or a unit struggling to defrost works harder and sounds it. See how to defrost a Comfortline.

For more on siting, flow and bypasses, read air source heat pump considerations and Can I add an air source heat pump to my hot tub?

Is the noise worth it?

For me, absolutely. My heat pump cut my hot tub running costs by 66%, and it heats the tub far faster than the old 3kW element did. The full story is in Why I fitted an air source heat pump to my hot tub and How I cut my hot tub running costs by 66%, and I’ve tested it in the cold in I ran my air source at -4°C. A bit of fan noise during heat-up is a small price for that. Just put some thought into where it goes.

If you’re choosing one, start with the ultimate guide to air source heat pumps for hot tubs and How to choose the right air source heat pump for your hot tub or pool. My Comfortline review covers the model I use.

Looking for a heat pump?

You’ll find the Comfortline range and the connection kits to plumb one in at parts4tubs.co.uk, and heating parts for US tubs at parts4tubs.com. If you’re still at the planning stage, my DIY hot tub plans show where the heat pump and control room go, so you can plan the noise out from the start.

FAQs

How many decibels is an air source heat pump?

Typically 40–60dB when running, according to the Energy Saving Trust. Hot tub heat pumps are usually quoted at 1m: the Comfortline 7kW is 38.8–50.2dB(A) and the 20kW is 45.3–57.1dB(A), from low speed to full power.

Is a hot tub heat pump louder than an air conditioner?

In my experience they’re similar, and my split-system air con actually seems a tad louder. Both are loudest at full power and much quieter once they’ve throttled back.

Will my neighbours hear my heat pump?

Possibly, if it’s close to their windows. In the UK, the benchmark is the level at 1m from a neighbour’s window: 42dB is the figure the Energy Saving Trust quotes, and England’s MCS 020 a) calculation works to 37dB(A). Distance and a solid barrier make a big difference.

Do I need planning permission for a hot tub heat pump?

Often not, but it isn’t clear-cut, because the permitted development rules were written for home heating heat pumps. If you’re near a boundary, in a conservation area or at a listed building, check with your council first.

Are heat pumps noisier in winter?

They can be. They work harder when the air is cold, and you’ll hear the defrost cycle every so often. The Energy Saving Trust says you can still hold a normal conversation next to one.

Got a heat pump already? Tell me how noisy yours is in the comments below. I read them all.

Cheers,
Andi

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Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi