Heat pumps could be the single largest step a household can take to reduce their carbon emissions while saving money on their bills. But many in Britain fear that, even though millions of homes across Europe have benefited from the shift away from gas or oil boilers, the UK’s draughty old homes could prove too great a challenge for the technology. The concern is unsurprising given that the UK has some of the least energy efficient homes in Europe. A study by the smart home company tado° monitored 80,000 users across Europe to find how quickly properties lose heat when outdoor temperatures fall to zero. It found that UK homes lost on average 3C after five hours without heating, compared with just 1C in Germany and 0.9C in Norway. The previous article in the series concluded that while in the vast majority of cases properties of any age can successfully make the switch from a gas boiler, improving insulation helps. So is it necessary to spend a lot on insulation and other mitigating measures to make a heat pump work? The claim Heat pump sceptics argue that while they might work in the well-insulated homes of Norway, Finland and Sweden, the UK’s relatively mild climate and historically high gas reserves have allowed energy efficiency standards to lag, meaning they will not be as effective in UK homes. The devices rely on a constant flow of gentle warmth to build up to the desired temperature, which the unconvinced argue is harder to achieve in a draughty home. Mike Foster, the chief executive of the Energy Utilities Alliance, a trade body that represents gas boiler manufacturers, told the Telegraph that the state of Britain’s housing stock meant heat pumps were unsuitable for up to 54% of homes currently using gas boilers without the eye-watering cost of retrofits. He argued that while many neighbouring European countries were “ravaged by war” in the 20th century and needed to be rebuilt, the UK still has “an awful lot of buildings built before 1919”, which mostly have solid walls. These can be particularly disruptive to insulate as doing so involves extensive building work. There can also be large upfront costs of for insulation of up to £12,000 when applied externally or £7,000 when added internally. “When you have external walls like that, they leak heat, and they’re not ideal for heat pumps,” Foster told the paper. While experts point out that leaky homes are not ideal for any kind of heating, will the switch to heat pumps necessitate Britain spending billions on insulation? The science Independent experts argue that households don’t need nearly as much insulation as they might think for a heat pump. A study of almost 750 UK homes previously referenced in this series by the independent research and technology organisation the Energy Systems Catapult (ESC), found that 85% of homes – from south-east Scotland and Newcastle to south-east England – did not require any extra insulation to have a heat pump successfully installed. About 15% of properties required some energy efficiency upgrades – but in the majority of cases this was loft insulation, which costs less than £1,000 and can be done with minimal disruption. Only “a few” propertiesrequired cavity wall insulation – which carries a cost of about £2,700 – or the replacing of old doors. This finding is backed up by UK data collected by Heat Geek, a startup that trains specialist heat pump installers and helps to match them with potential customers. From a dataset of more than 100 properties it found that heat pumps were still able to warm uninsulated homes more efficiently than gas boilers. In one example, a mid-century, mid-terrace house with uninsulated cavity walls recorded a heat pump efficiency score of 4.99 (a score of 3 or above means the device is cheaper to run than a gas boiler). Heat Geek found even a detached home built before 1900 with uninsulated solid walls recorded an efficiency of 4.24. Both homes had loft insulation. Andrew Sissons, a deputy director at Nesta, a charity which undertakes research into home heating innovation, said: “Insulation is a good thing to do in its own right – but your home doesn’t need to be insulated to get a heat pump.” A well-insulated home can make heat pumps run more efficiently but it is more important to make sure that the correct size heat pump and radiators are installed, he said. Some of the least disruptive and lower-cost insulation measures, such as draught proofing and loft insulation, can offer significant energy savings, he said. Meanwhile, more disruptive measures, such as solid wall insulation, are expensive and do not always justify their cost in terms of the savings that can be expected – both in terms of cash and carbon emissions. The caveats Home insulation upgrades are unlikely to be as expensive as heat pump sceptics suggest – but that doesn’t mean that the price of relatively low-cost improvements to radiators and a new water tank don’t still add up. For the 750 homes in the ESC study which installed a heat pump, the total cost was about £14,800 – including the pump, any home upgrades and installation costs. The government’s £7,500 grant towards this work helps, but for many households this upfront cost would pose a financial challenge. There are also a number of home improvement costs that may be non-negotiable for a heat pump to work effectively: larger radiators, a hot water tank and updated pipework. Not all homes require a radiator upgrade but in the ESC study, 93% of homes had theirs replaced as part of the heat pump installation. It also found that 81% had a hot water tank fitted. The need to upgrade old pipework is far less likely. A minority of homes built in the late 1980s and early 1990s were fitted with “microbore” pipes with a diameter of under 15mm. These were compatible with gas boilers and cheaper and quicker to install than a full-sized pipe system. If you are unlucky enough to have these in your home they will need replacing, because heat pumps run at a flow temperature of about 40C, compared with a gas system’s 50-60C . Therefore they require larger pipes to allow for greater volumes of water to transmit heat around the home. This is also why larger radiators and underfloor heating – which have a greater surface area – can make an important difference to how well a heat pump system performs. A study by Fraunhofer-Gesellschaft, an applied research organisation, revealed that heating systems which included underfloor heating achieved an efficiency rating of between 3 and 5 while households with radiators only fell between 2 and 4. So are there homes which should not install heat pumps until they’re properly insulated? Yes, says Sissons. These are households struggling with fuel poverty. They should first take advantage of the government funding available to low-income and vulnerable households to improve their insulation at no cost. This would bring immediate benefits to the household – in lower bills and a warmer home – and make it easier to design a heat pump system which can deliver the largest possible cost savings over the long-term. The verdict If you currently live in a home where the heating system keeps rooms comfortably warm, it is very likely that you won’t need to undertake any extra insulation before installing a heat pump. A certified installer can give advice on each individual property. However, if you can afford to invest in low-cost measures like draught exclusion, double glazing and loft insulation, you would get this money back in lower bills over the long term. If you live in a poorly insulated home and are on a low income, you should check whether you are eligible for Great British Insulation – the government scheme that could pay for your insulation as well as covering a new heating system from a qualified installer.