Boilers will be replaced by heat pumps but it’s a marathon, not a sprint

If Bill Gates and Boris Johnson agree on something it must be a good idea – or perhaps not, depending on your assessment of those two gentlemen. But does that mean we should all be buying electric cars or ditching the gas boiler for a heat pump?

The £400m partnership to boost green investment is straightforward enough, though that amount is not large in the context of either Bill Gates’s wealth of close to £100bn, or the UK government’s budget deficit. The plan to give householders grants of up to £5,000 to put in heat pumps is more complicated.

Climate change campaigners feel this programme does not go far enough, as the costs of installation range from £6,000 to £8,000 for air source pumps to £10,000 to £18,000 for ground source ones. But the issue is not only one of cost, it’s also of practicalities.

Heat pumps are an excellent and established technology but they need space, and not all homes have that. There is a parallel with electric cars. The technology is simpler and more reliable than internal combustion engines. The costs are coming down, and they will be cheaper than petrol or diesel cars by 2027. People who have them love them. But while charging them is fine for people who have a garage or a driveway, it is not so easy for anyone who lives in a flat or has to park in the street. Public charging points are being rolled out, but the infrastructure is still inadequate.

Something similar applies to heat pumps. The technology is even more established than electric cars, for it has been around for at least a century. Air conditioners – which are air source heat pumps running in reverse – became popular in American homes from the 1960s onwards. Ground source heating for homes was developed in the 1980s in Sweden, which supplies many of Europe’s heat pumps now.

They work very well. On a personal note, we’ve had one in Scotland for more than a decade. As a general rule, the lower running costs mean that the additional cost of installation can be recouped in somewhere between 10 and 20 years. But while it makes sense for developers to build heat pumps into new homes because the cost is relatively small compared with all the building expenses, switching to heat pumps in an existing house or flat is not such an obvious choice. And it is existing homes that the government is targeting with this plan.

To put in ground source heating, you need the ground to lay the pipes in trenches a metre deep to collect the heat. Think of the area of a tennis court. You can dig a borehole, but that is very expensive as you may need several and they have to be 100m deep or more. You need space inside your home, as the unit is the size of a big American fridge rather than a gas boiler hung on the wall. And since the system runs cooler than regular boilers, you will need larger radiators.

If ground source is impracticable, there is air source, where the heat is gathered from the air. This means a fan in a box outside somewhere. It works perfectly well (we have one too), except that it is less efficient than ground source, particularly in cold weather when you need heat most. You also have the noise of the fan to think about.

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So what’s the verdict? Anne-Marie Trevelyan, the international trade secretary, said that this plan is a first step and that switching could take 15 years. That makes sense. Heat pump technology will advance, costs will come down, installers will gain experience in how to instal the kit more swiftly, and the country will have more electricity generating capacity to drive the systems.

You get about three times as much heat per unit of electricity from a heat pump than you do from ordinary electric heaters, but they do use power. If, in addition, we are all going to drive electric cars, the country will need a lot more supply. All those solar panels on roofs help a bit, but we will need much more – and we will need it when the sun does not shine and the wind does not blow.

We will make this switch. The entire developed world is making the switch. But there is a huge argument for doing so in a measured, step-by-step manner. This is a marathon, not a sprint.