The October 2023 increase in Boiler Upgrade Scheme vouchers raised monthly heat-pump installations in northern England by 24% relative to Scotland's trajectory, according to research by LSE, Imperial College London and UCL. The estimated effect equals about 7,200 additional units over the following 20 months, based on 260,000 certified installation records.
The design uses an institutional difference. BUS applies in England and Wales, while Scotland runs separate schemes whose support levels did not change in October 2023. Comparing English and Scottish trends helps isolate the voucher increase from common forces such as energy prices, weather, interest rates and rising awareness of the technology.
On October 23, 2023, support for air-source heat pumps rose from £5,000 to £7,500 and ground-source support from £6,000 to £7,500. An accredited installer applies for the voucher on a household's behalf and deducts it from the invoice. The policy therefore attacks upfront cost, a visible barrier to replacing fossil-fuel boilers.
The evaluation also asks who captured the subsidy. Critics feared installers would raise prices and absorb the extra £2,500. The authors found the opposite: a larger local market attracted suppliers, competition lowered prices and households appear to have saved more than the grant increase itself. That mechanism distinguishes an incentive that expands supply from one that simply raises margins.
The 24% figure is not a uniform UK-wide increase or the share of homes leaving gas. The sample covers certified installations in northern England and Scotland, the comparator has its own policies and the post-reform window is 20 months. The inference assumes sufficiently parallel underlying trends; later work should test persistence, distributional effects and places outside the sample.
A heat pump does not automatically guarantee lower bills or emissions. Outcomes depend on building insulation, equipment sizing and configuration, installation quality, electricity tariffs, operating temperature and the generation mix. Grants address part of capital cost but need technician training, consumer protection, clear advice and tailored support for difficult buildings and households unable to advance money.
Similar capital grants operate in 22 European countries and in the United States, Canada, China, Japan and Korea. The transferable lesson is not a single voucher amount but the interaction of generosity, stability, installer capacity and competition. If the effect persists, the UK case shows that larger support can accelerate adoption and lower prices; a just transition must also reach those currently excluded.
