Summer 2024 saw the UK’s hottest June on record, with temperatures hitting 30°C in London and Manchester. Sales of portable air conditioning units jumped 40% year-on-year, according to Currys. For the first time, cooling is not a luxury in this country — it is becoming a necessity for many homeowners, especially those in south-facing flats or poorly insulated Victorian terraces.
Yet the environmental cost is rarely discussed. As The Guardian reported last week, the question is no longer whether you should get air conditioning, but how to do it without doubling your carbon footprint or your electricity bill.
What it costs a typical 3-bed semi
A portable AC unit rated at 2.5 kW typically uses 1 kWh of electricity per hour. At the current price cap of 24.5p per kWh (from October 2024), that is 25p an hour. Run it for eight hours a day over a 30-day heatwave — £60. Add standing charges and you are looking at £70–£80 per summer month. For a whole summer (June–August), £200–£250 is realistic.
But most homeowners buy undersized units. A 3-bed semi of 80 m² needs at least 3.5 kW of cooling capacity. That unit will pull 1.5 kWh per hour, pushing the summer cost to £300–£400. And that is before you factor in the extra electricity for fans to circulate the cold air — another 50W per fan, negligible but additive.
The green alternative: reversible heat pumps
Air source heat pumps already installed for heating can reverse their cycle to provide cooling. They do this by running the refrigerant backwards — extracting heat from inside the house and dumping it outside. The efficiency is roughly three times that of a portable AC unit: for every 1 kWh of electricity, you get 3 kWh of cooling, compared to 1 kWh from a standard unit.
The catch is installation cost. A heat pump costs £7,000–£13,000 installed, depending on the size and whether you need new radiators or underfloor heating. The Boiler Upgrade Scheme offers a £7,500 grant towards heat pumps, but only for heating, not cooling. If you want both, you pay the full cost upfront. Still, for a household that also replaces a gas boiler, the payback on heating alone is 10–15 years — and cooling is a free bonus.
But there is a second catch: not all heat pumps are designed for cooling. Some models require a reversing valve; others need a buffer tank or a different refrigerant. You must specify the cooling function at the point of purchase. Retrofitting it later costs £1,000–£2,000.
Who qualifies — and who doesn’t
The Energy Company Obligation (ECO4) does not fund air conditioning. It covers insulation, heating upgrades, and draught-proofing for low-income households. However, better insulation reduces the need for cooling. A well-insulated loft and cavity walls can cut indoor temperature by 2–3°C during a heatwave, according to the Energy Saving Trust. That alone might make AC unnecessary.
For those who must cool, the greenest option is solar panels. A typical 4 kW system (10–12 panels) generates 3,400 kWh per year — enough to run a portable AC unit for 1,000 hours, or a heat pump for 3,000 hours of cooling. Installed cost is £5,000–£6,500, with a payback of 8–12 years at current electricity prices. No grant exists for solar cooling specifically, but the 0% VAT on solar panels applies to any electricity used in the home.
So what should you do?
If you already have a heat pump, check whether it can reverse. If it cannot, consider upgrading to a model that does — the cooling function adds £500–£1,000 to the upfront cost but saves £150–£200 a year on summer electricity. If you do not have a heat pump and are considering one for heating, spec the cooling function now. It is cheaper to include it at installation than to retrofit.
If you simply want a portable unit for one room, buy the smallest unit that meets the room size (measured in BTUs: 1 kW ≈ 3,412 BTU). Run it only when the room is occupied, and close curtains during the day to reduce solar gain. And if you are on a standard variable tariff, consider switching to a time-of-use tariff like Economy 7 or Octopus Agile, which offers cheaper electricity at night — you can pre-cool the house then.
Households on standard variable tariffs can apply for a heat pump quote through the Boiler Upgrade Scheme from 1 November 2024. Eligibility closes when the scheme’s budget runs out — typically within the first few months. Act before Christmas if you want the £7,500 grant.
Frequently Asked Questions
It depends on the unit. Portable ACs use hydrofluorocarbon (HFC) refrigerants, which are potent greenhouse gases if leaked. Reversible heat pumps use lower-GWP refrigerants and are three times more efficient. Solar panels can offset the electricity use entirely, making cooling carbon-neutral in operation.
No current UK government grant specifically covers air conditioning. The Boiler Upgrade Scheme subsidises heat pumps for heating only. ECO4 funds insulation that reduces cooling needs. VAT on solar panels is 0%, which can indirectly offset AC electricity costs.
