By the end of the decade, well over 60m heat pumps could be warming homes across Europe, according to industry figures, as government policies target household carbon emissions.
In the UK, the newly appointed energy and net zero secretary, Ed Miliband, has committed to maintaining the heat pump grants offered by the previous government to help to accelerate the rollout of the technology.
The total effect of this switch away from fossil fuel heating to low-carbon alternatives could cut CO2 emissions across Europe by 46%, but critics of the technology point to another cumulative impact: noise.
Heat pumps are designed to be installed outside the home to extract warmth from the air, ground or water. In densely populated areas, this could mean scores of heat pump fans humming within a small area.
One device typically emits a constant hum of between 40 and 60 decibels – about the same as a fridge or dishwasher – but could millions of heat pumps amount to a noise nuisance?
The claim
Concerns about heat pump noise began to take hold in the British press late last year after the Conservative government commissioned an independent review into noise emissions from air source heat pumps.
Research submitted included a report by three experts presented at the Institute of Acoustics conference last October. It was seized on by the Daily Telegraph, which reported that it had found heat pumps were “too noisy for millions of homes in the UK”.
The report contained a claim that heat pumps installed in flats or terraced houses would break the noise limits set by the Microgeneration Certification Scheme (MCS), an accreditation body, which stipulate that a heat pump should be no louder than 42 decibels within one metre of a neighbour’s door or window.
The Daily Mail and Daily Express repeated the story a day later. Concerns about the issue appeared in the Guardian, too, with one reader’s letter complaining that a summer stay in a development where all eight properties had heat pumps was marred by the devices. “If you sat in the garden in the evening, it was an annoying, continual source of noise,” the writer said.
The science
The main source of heat pump noise is the fan, which draws in air, and the compressor, which raises the temperature of the refrigerant by increasing pressure on its gases. (You can read more about exactly how a heat pump works here.)
Typically an air source heat pump will run at a decibel level of about 40, but it can reach 60 on particularly cold days when it needs to work harder to draw extra heat from the air. This would put it in a similar noise range as a fridge – or a gas boiler.
Older devices have typically been noisier than the latest ones. Some manufacturers produce low-noise heat pumps, which sacrifice a little in terms of efficiency to offer a quieter experience.
The Guardian reader’s experience may have been due to improper installation or the use of older, noisier heat pump models, according to Jack Harvie-Clark, a director at Apex Acoustics. “Modern heat pumps can be significantly quieter, and proper placement – away from property boundaries – can further reduce noise impact,” he said.
Apex was one of the consultancies behind the report cited by the Telegraph. It was quick to rebuff the coverage, describing its “misleading” claims that heat pumps were too noisy for millions of UK homes as “an exaggeration”.
“While noise is a valid concern … technology improvements and proper installation can mitigate noise issues in most homes. The article presents noise as an insurmountable problem, which is not the case,” the company said, pointing out that there were many homes – typically detached and semi-detached properties – where there would be no problem at all.
Last November the UK government published the results of its review, which found that noise emissions were a concern for a minority of consumers, with a low incidence of complaints. In the chancellor’s autumn statement later that month, it was announced that the government would consult on changing rules that apply in England, including removing the one-metre boundary rule.
The government’s research included a survey of households living within 50 metres of a heat pump, across 60 areas with high heat pump uptake, to gauge noise nuisance inside the house.
It asked respondents to specify which neighbourhood noises could be heard from indoors. Heat pumps received one of the lowest number of mentions, while dogs topped the list. The study found that 57% of the 139 respondents noticed barking during the day, and just 4% noticed the sound of a heat pump.
Harvie-Clark has done further research on the issue for Nesta, an innovation charity, which is due to be published this month. Its findings suggest that even in worst-case scenarios with high housing density and all air source heat pumps operating simultaneously at maximum permitted sound power levels, the cumulative noise impact was not likely to be more significant than the individual noise impact of the nearest neighbour’s heat pump.
“I’ve also investigated in detail how some other European countries manage noise from air source heat pumps,” Harvie-Clark said. “Most have higher noise limits in the daytime and some, but not all, have slightly lower limits in the night-time.
“We [in the UK] have one noise level limit for all times, which to me seems clumsy. The main manufacturers see northern Europe as one market, so they all have controls that can limit operation to lower noise levels at night-time
The caveats
Although potential noise issues can be mitigated, Harvie-Clark believes that more work should be done to understand the impact of heat pumps as they gain popularity across Europe, and he has stressed that consumer education is key to ensuring that the right heat pump is installed in the right way.
For example, the government’s review of whether heat pump noise is noticeable has some notable limitations: heat pumps are not widely used, so even an area of “high density” will include fewer heat pumps than there will be in the future.
There are other issues with the way noise limits are characterised. For example, a heat pump’s defrost cycle, which is louder than its normal running level, is not included in MCS’s noise tests.
“Nor is low-frequency noise, nor any information on tonality or directionality,” said Harvie-Clark. “So these things cannot by definition be taken into account in any calculation or assessment prior to installation.”
The verdict
Heat pumps are quieter than they used to be, and getting quieter still. But better consumer information could go further in mitigating the overall impact of noise by choosing the best model for the home and using it correctly.
“I believe that many people in the UK try to operate their heat pumps the way they operate gas boilers – turning them on and off – but they can’t heat houses as quickly as gas boilers, so they need to run constantly to do that,” said Harvie-Clark.
Turning heat pumps on after a period of being off will require the machine to work harder and therefore create more noise. So taking a slow and steady approach to home heating can make heat pumps more efficient, and quieter, too.
“In colder European countries they accept that this is how to run heating systems. Our temperate climate means people have different control expectations,” Harvie-Clark said.
“While the potential noise impact of air source heat pumps should be considered, it is important to balance this with the significant environmental benefits of transitioning away from fossil fuel heating systems. Gas boilers also make a noise.”
