A Heated Debate

Spread the love

From Climate Scepticism


Pumping it up again

In Hot Off The Press I reported on a Guardian article that appeared on 30th May this year, seeking to spin a survey on heat pumps. To my mind, the survey was much more equivocal regarding satisfaction with heat pumps than the Guardian piece suggested. Well, now they’re at it again, with another article, with the heading “Heat pumps twice as efficient as fossil fuel systems in cold weather, study finds” and sub-heading “Doubts about whether heat pumps work well in subzero conditions shown to be unfounded, say researchers”. The article is based on a study with the title “Coming in from the cold: Heat pump efficiency at low temperatures”.

The article claims that research shows heat pumps to be more than twice as efficient as fossil fuels at low temperatures, out-performing oil and gas heating systems even at temperatures as low as -30C. The UK is falling behind with regard to the heat pump roll-out (you can say that again), and it’s because people have been scared by false information regarding their efficacy at low temperatures. We are also told:

The UK government is consulting on proposals for incentives to households to take up heat pumps, which at about £7,000 or more can cost two or three times as much up front as gas boilers. Boiler companies are also to be penalised if they fail to sell enough heat pumps, under a “market-based mechanism” that will require them to sell a certain quota of heat pumps or pay a penalty.

Some proponents of gas boilers have railed against the quota, which they claim will add costs to consumers, and at least one boiler company has responded by telling customers that the price of new gas boilers is likely to go up as a result of this green measure.

The second of those two paragraphs is more than a little strange, carrying with it the implication that the proponents of gas boilers and “at least one boiler company” are somehow behaving badly in making such claims, since it’s abundantly obvious that the “claims” (note the loaded language) are clearly correct.

Be that as it may, we should look at the survey which provided the hook on which the Guardian hangs yet another heat pump article. It was published on 11th September 2023, and has four co-authors. The first named are Duncan Gibb, “a senior advisor at the Regulatory Assistance Project (RAP), a global team of highly skilled energy experts with a focus on heat decarbonization policy”, and Jan Rosenow, also of RAP. RAP, according to its website is “an independent, global, non-governmental organization advancing policy innovation and thought leadership within the energy community.” Independent, perhaps, but with a very definite interest in pushing things like heat pumps:

For more than three decades, RAP has been a leader in developing solutions to the world’s most pressing power sector challenges. In the next five years RAP will focus on key policy areas to drive a more efficient and equitable decarbonized energy future and to ensure a sustainable and just transition: Accelerate electrification of buildings and transportation; accelerate the phaseout of gas infrastructure; remove barriers to distributed energy resources; and decarbonize the electric grid.

Messrs Gibb and Rosenow regularly write articles extolling the virtues of heat pumps, such as How the energy crisis is boosting heat pumps in Europe and How to solve the UK’s heat pump problem.

The two other authors are Dr Richard Lowes (also of RAP) and Professor Neil Hewitt, Head of School at the Belfast School of Architecture and Built Environment at Ulster University.

All four gentlemen are highly qualified and knowledgeable about heat pumps. I think it’s probably also fair to say that they are all rather keen on decarbonisation generally, and heat pumps specifically. Not that this in any way invalidates their research and findings, but when analysing their study, I think it’s worth bearing in mind that they may start with a predisposition to encourage heat pump take-up.

As the introductory paragraph makes clear, the object of the study is to analyse “field studies with real-world performance data of air-source heat pumps” with a view to responding to the suggestion “that heat pumps cannot deliver useful efficiencies at lower temperatures.” Perhaps I am being unkind, but it seems to me that the starting-point is to seek evidence that will help to debunk criticism of the efficacy of heat pumps when the temperature is very low (i.e. precisely when a good heating system is most needed). In the words of the authors, their “commentary responds to this question”. And this is the conclusion:

It finds that well below 0°C, heat pump efficiency is still significantly higher than fossil fuel and electric resistive heating systems at an appliance level. The standard heat pumps investigated in this commentary demonstrate suitable coefficients of performance for providing efficient heating during cold winters where temperatures rarely fall below −10°C, i.e., most of Europe.

I accept that finding at face value, of course. However, there are issues that suggest that notwithstanding the findings, heat pumps really are not the answer for many UK householders, though the study does not mention these, or at least, insofar as it does, it doesn’t draw that conclusion. The first issue is with regard to the price of gas and electricity for UK domestic consumers. A quick visit to a price comparison website suggests that electricity in the UK currently costs domestic consumers somewhere between 26.6p and 28.67p per Kwh, with an across-the-board daily standing charge of 42p. For gas, the daily standard charge is set at two-thirds that level, at 28p. However, the Kwh charge is much cheaper, with prices ranging from 6.46p to 7.21p. Roughly speaking then, electricity is around four times as expensive as gas to use, with a daily charge that is 50% higher. Ignoring the costs of changing a gas boiler for a heat pump (though in the real world, such a cost is all too relevant), installing a heat pump would seem to make sense for most householders only if a heat pump’s efficiency was four times greater than the efficiency of a gas boiler (all other things being equal). Does the study find this to be the case? This is the finding:

Heat pump efficiency is measured by the device’s coefficient of performance (COP), the ratio of the useful heat outputted to energy consumed. Typical COP values for heat pumps lie in the range of 3–6, indicating that 3 to 6 units of heat are created from each unit of electricity used. A year-round average COP of 3–4 is common for household applications.

If I understand it correctly, the COP of a standard gas boiler is around 0.9 (see, e.g. here). And so, all things being equal (except that they’re not), at first blush the heat pump might seem to pass that test. But even then there’s a problem:

The temperature difference between a heat pump’s source (the outside air) and sink (heating supply location) plays a determining role in the COP and, therefore, its overall performance. If the source temperature dips and the sink temperature is maintained, the COP falls. Around freezing temperatures, air-source heat pumps also can experience a reduction in COP due to the defrosting of external components.

That “year-round average COP of 3–4” for heat pumps is just that – a year-round average. In warm summer weather (when the heat pump is little-used, if it is used at all), the COP will be above that figure. And in cold winter weather (when the heating source is most urgently required) the COP will be below that figure – and the colder it gets, the lower the COP will be. In fact, we are told:

When the outside temperature was between 5°C and −10°C, the mean COP across all systems was 2.74 and the median was 2.62, sufficient to meet heating loads at much higher efficiency than fossil heating and electric resistance heat alternatives.


Below 0°C, the COP maintains a level well above 2 in all cases, meaning that an air-source heat pump would operate at more than twice the efficiency of combustion or resistive electric heating technology.

Thus, even though heat pumps do “demonstrate suitable coefficients of performance for providing efficient heating during cold winters”, and even though they may be wonders of efficiency, they will still be significantly more expensive than gas boilers to use in winter for the average UK householder (up to twice as expensive).

The study seeks to justify the underlying theme that heat pumps are fine in cold countries, by including statistics demonstrating high heat pump penetration in Estonia and in Scandinavian countries. But we are told nothing about energy pricing in those countries, and the authors go on to concede that “[t]he data do not provide insights about the achieved efficiency of those heat pumps” while nevertheless optimistically inferring that “the large share of household installations suggests that heat pumps can effectively provide heating in colder climates.

Perhaps the optimistic inference is justified, but in order to establish that, we would need to know much more about the nature of the housing stock in those countries compared to the state of the UK’s housing stock. Surprisingly perhaps, I can see scarcely any attention paid to this issue at all. Instead, there is an almost throwaway remark to the effect that:

In any case, to mitigate the impact of peak heating loads on energy systems, efforts can be made toward improving the performance of the building stock to minimize load and level off heating demand peaks, as well as encourage demand response.

And as to the claim that “that heat pumps can be successfully installed in these conditions without concerns over performance or the need for back-up heating capacity”, that is subject to this rather important, but casually mentioned caveat:

This is subject to thorough heating system design and a high-quality installation in a building.

Further, as I mentioned above, all things are not equal when comparing heat pumps with gas boilers. Much of the UK’s housing stock is old and badly insulated. Much of it would need expensive works to be implemented before heat pumps could be installed and provide adequate heating. As the Homebuilding website I referred to above says:

Ultimately, if you opt for a heat pump rather than a gas boiler, you will need to size the radiators and/or UFH pipe lengths very precisely. You will also need to be able to control the speed of the water in the circuit as well as the delivery of heat to the circuit. The balance is critical and certainly not always possible in older or ‘energy hungry’ properties.

So, if you ask yourself ‘should I swap my gas boiler for a heat pump?’, you need to be aware that you’ll likely need to update your existing radiators and pipework, as well as your heat source, in an existing home.

The study concludes with a statement that the authors declare no competing interests, but also with an acknowledgement that “[t]his work was funded by a grant by the Crux Alliance.” Of course, the source of funding doesn’t invalidate the study’s findings, but it’s perhaps worth noting that the Crux Alliance (as its website puts it) is:

…a group of globally recognized, technically expert organizations that are laser-focused on advancing policies—unbiased, pragmatic, and localized—to generate powerful action in the countries and sectors that matter most for carbon reduction. The members of the Crux Alliance, known as Crux Policy Centers (CPCs), support policymakers around the world working to retire polluting power plants and to replace polluting vehicles, factories, and buildings with low-carbon alternatives—and to grow these alternatives at speed and scale. The Crux Alliance is all about getting climate policy right, right now.

In other words, it might not be too unfair to say that it has a policy position that is probably keen to encourage (among other things) the uptake of heat pumps.

As I see it, the study makes the case that heat pumps can work in cold temperatures, and that in some countries with cold winters they are widely used. It does not go on to make the case that it makes financial (or any other) sense to encourage a large-scale swapping of gas boilers for heat pumps in the UK, with its often inappropriate housing stock, expensive electricity (compared to the price of domestic gas) and high up-front costs. I see nothing in it to justify the tenor of the Guardian article reporting on it, to the effect that the UK should “bring in new measures to roll them [heat pumps] out as rapidly as possible.