How noisy are heat pumps compared with a gas boiler?

There is also a legal backstop that boilers do not have. In the UK, the noise limit for a heat pump is 42 decibels, measured one metre from a neighbouring window, and an installation that exceeds it needs planning permission². So while the two technologies are broadly comparable in decibels, a heat pump's noise is regulated in a way a boiler's is not.

Why noise puts people off heat pumps

Noise is one of the biggest psychological barriers to switching. In the Quiet Mark YouGov UK National Noise Survey 2026, 63% of respondents said noise concerns would influence their decision to install a heat pump⁶. Uncertainty compounds this: in a Which? survey of heat pump considerers, over a third (37%) said they don't know if a heat pump will perform better than a gas boiler⁸. People who cannot picture how the technology will sound, or how it will behave, tend to stick with what they know.

The irony is that the noise comparison usually favours the heat pump. Because the noisy parts sit outside, the sound a household actually lives with indoors is often lower than a boiler's, and one household that replaced its boiler reported that indoors the new system was "not louder than the boiler was"⁹. What drives hesitation is less the measured decibels than the fear of an unfamiliar hum outside a bedroom window, which is why siting, covered below, matters more than the headline numbers. Cost and electricity prices also lead people to favour gas boilers, so noise sits within a wider set of doubts¹⁰.

Decibel levels explained

The typical range of a heat pump when it is on is between 40 and 60 decibels². Air source heat pumps create between 40 and 60 decibels on average, a similar noise level to a dishwasher or microwave³. Citizens Advice describes the heat pump unit as usually quiet, about the same noise level as a fridge¹¹. Those comparisons are more useful than the raw numbers, because decibels are logarithmic and most people have no feel for them: what matters is that a heat pump sits in the same band as ordinary kitchen appliances, not next to a lawnmower.

The 42 decibel figure works differently. It is not a measurement of the unit itself but of the sound reaching your neighbour: you can't normally install a heat pump unless the noise level is 42dB or less when stood one metre from a neighbouring window of a habitable room². Croydon Council's guidance states the same figure as the legal noise limit for heat pumps in the UK⁵. A boiler faces no equivalent test, which is why heat pump noise assessments, not boiler ones, are part of the installation process.

Sources of noise in heat pumps versus boilers

A heat pump's noise comes from its moving parts: the fan that draws air through the outdoor unit and the compressor that drives the refrigeration cycle. Council guidance notes that the external fan units can generate a considerable level of noise¹². The character of the sound is a steady hum plus airflow, with startup sounds when the unit begins a heating cycle. One homeowner with a Samsung unit reported hearing it all the time in the living room, sometimes quieter and sometimes louder, and whooshing and startup sounds that disturbed sleep in a bedroom above the outdoor unit¹³. That is the bad case, and it is usually a siting problem rather than a loudness problem.

Indoors, the picture varies by type. Air-to-air heat pumps have indoor units, and these can be noisier than other heat pumps¹⁴. In one Energy Saving Trust case study, the indoor unit of the heat pump typically made the same level of noise as a gas boiler when running¹⁵, while in another, both the outdoor and the indoor unit were noisy while operating¹⁶. A gas boiler's noise, by contrast, comes from its burner firing, its circulation pump and the flue, all inside the house, and a boiler that becomes suddenly noisier is generally treated as a fault to be checked. Neither technology is silent; they simply put their noise in different places.

How placement and fitting influence sound levels

Because the 42 decibel test is measured at a neighbouring window, siting is the main lever an installer has. The MCS 020 noise assessment, which every compliant installation should use, records the installation address, the heat pump installation location, and a description of the assessment position, with four assessment positions per assessment for a single unit, and separate assessments for two or four heat pumps where more than one is installed¹⁷. Barriers such as open fencing can be included in the calculation¹⁷, which is how installers demonstrate compliance on tighter sites.

The rules that follow from the assessment are strict. Bedford Council's guidance states that noise levels for an air source heat pump on its own must stay at or below 42 decibels from a metre distance away from any habitable room¹⁸. New Forest Council requires compliance with the Microgeneration Certification Scheme Planning Standards (MCS 020) in order for the unit to be permitted development, because air source heat pumps can be noisy¹⁹. If the noise level is exceeded, planning permission approval is needed¹⁸. More detail is in our pages on MCS 020 noise assessments and where a heat pump outdoor unit can go.

Heat pump noise after dark

Yes, an air source heat pump runs whenever the home calls for heat, including overnight, and the outdoor fan is audible whenever it does. For light sleepers this is the sharpest edge of the comparison with a boiler, whose outdoor noise is limited to flue gases. The homeowner account above, with a bedroom directly above the outdoor unit, shows what happens when night running and poor siting combine¹³.

The main escape routes are technology and siting. Ground source heat pumps are generally even quieter than air source units, because there is no outdoor fan at all¹, and an official consultation on refrigerant rules likewise notes that they are quieter and offer increased energy efficiency²⁰. Our ground source heat pump guide covers the trade-off, which is mainly cost. Within air source, placing the unit away from bedrooms, and checking the night-time noise assessment before installation, is what stands between a faint hum and a disturbed night.

Comparing efficiency and running costs

Noise is only one half of the comparison; the other is what each system does with the energy it burns. Electric heat pumps use about 3 to 4 times less energy than gas boilers to produce the same heat⁷, because a boiler produces less than one unit of heat for each unit of gas it uses²¹, while a heat pump moves heat rather than generating it. Building regulations require each gas boiler to have a minimum efficiency of 86%²², which is the legal ceiling on what a boiler can do.

Running costs are a different question from efficiency, because electricity costs more per unit than gas. At current energy prices, running costs for heat pumps are around the same as for a new gas boiler², and when switching from a gas boiler, bills will likely stay similar under current tariff caps²³. It is typically more expensive to run a heat pump than a gas boiler because of the relative price difference between electricity and gas²⁴, but on a heat pump time-of-use tariff, running costs can be reduced significantly, and a heat pump can cost less to run than a gas boiler²⁵. Which? quotes Dr Jan Rosenow: "A household could save more than 50% on running costs with a heat pump compared to a gas boiler. But this requires the" highest quality installation, high efficiency and a heat pump tariff³. The full breakdown is in our heat pump vs gas boiler running costs page.

New gas boiler ban and your choice of heating

The government has said it plans to phase out the installation of gas boilers in new homes beyond 2035²⁶, and gas boilers are being phased out from new builds from 2025²⁷. For existing homes, the direction of travel is the same but slower, and there is no forced removal of boilers already installed. A replacement gas boiler will probably have to be a condensing boiler unless there is sufficient reason why one cannot be installed, fitted by a Gas Safe registered installer²², so the gas option remains open for households not ready to switch.

That does not mean the switch is painless for everyone. An official report on the heat pump transition found that households replacing previously working gas or oil boilers were more equivocal, more likely to report an increase in bills, and typically expressed a preference for a new boiler over the heat pump²⁸. Against that, if your boiler is old, a heat pump is a much lower carbon alternative to a new boiler²⁹, with up to 70% less CO2 over 15 years than a gas boiler and zero emissions at point of use³⁰. Noise, cost and the 2035 timetable all point the same way: the decision is coming for every household, and the households that research siting and tariffs now are the ones that end up satisfied. Our pages on replacing a gas boiler with a heat pump and the full heat pump guide take the comparison further.