Energy bill-payers will be asked to subsidise the installation of tens of thousands of new gas boilers across the UK under government plans, at a time when experts say gas boilers should be urgently phased out.

Experts said it was baffling that ministers should be promoting the installation of new fossil fuel boilers, instead of low-carbon dioxide alternatives such as heat pumps.

At least 20,000 new gas boilers will be installed under the energy company obligation (Eco) scheme, which requires energy companies to fund improvements that should cut greenhouse gas emissions. The long-running scheme has been criticised in the past for providing discounts to well-off households to replace ageing gas boilers with more efficient models, rather than focusing on more difficult but more effective improvements, such as helping low-income households with home insulation.

In a consultation document, slipped out this summer without fanfare, the Department for Business, Energy and Industrial Strategy laid out plans for how the Eco should work from March 2022 to March 2026. The government’s “preferred option”, shown in the 62-page document, is for 20,000 new gas boilers to be installed in homes that currently lack central heating.

A further 25,000 homes will have broken heaters repaired or replaced, which could also involve the repair of gas boilers or the installation of new ones.

Government plans to reduce emissions from home heating, which accounts for roughly 14% of the UK’s overall emissions and have remained stubbornly high despite two decades of efforts to reduce them, have been in disarray since the failure of the green homes grant earlier this year.

Under the GBP2bn green homes grant, announced last summer as part of the prime minister’s promise to “build back greener” from the Covid-19 pandemic, at least 600,000 homes were supposed to be upgraded with insulation, heat pumps and other low-CO₂ improvements. But the scheme was beset by administrative problems and fewer than 50,000 households received the help envisaged. The scheme was scrapped after less than six months.

A new heat and buildings strategy has been in preparation for months, but has yet to be published, although time is running out before the UK hosts the Cop26 UN climate talks in Glasgow this November, at which all countries will be asked to come up with concrete plans for slashing emissions.

Ministers are understood to be nervous about proposals that would require all households with gas boilers – the dominant form of home heating in the UK – to rip them out and replace them in the next decade. The Treasury has also blocked proposals to subsidise the switch to low-CO₂ heat pumps or electric boilers, and calls for ministers to ban new gas boilers from 2025.

Experts said the effective subsidies for new gas boilers ran contrary to the government’s targets on cutting greenhouse gas emissions, by 68% by 2030, and by 78% by 2035, compared with 1990 levels.

Jess Ralston, analyst at the Energy and Climate Intelligence Unit, said: “While it’s important that vulnerable households are supported in staying warm at home, installing new fossil fuel boilers – which contribute to harmful air pollution in homes that are already more likely to have poor air quality – just means that fuel-poor families are locked into dirtier, more expensive and more unhealthy heating systems for longer. It’s wasteful and baffling when it’s clear that a clean heating revolution is just around the corner and gas prices are rocketing.”

Parallel plans for improving the energy efficiency of social housing have ruled out fossil fuel boilers, in favour of low-CO₂ alternatives.

“Making this the norm – instead of continuing to rely on outdated, unhealthy and inefficient technology – would help boost the government’s credentials on green homes while placing households suffering from fuel poverty in prime position for Britain’s cleaner, healthier heating future,” Ralston added.

Jan Rosenow, Europe director at the Regulatory Assistance Project, said: “Paying people to install new heating systems running on fossil fuels is incompatible with the UK’s climate goals. Rather than subsidising gas boilers we urgently need a policy to support the transition to clean heating. Other countries have stopped funding new fossil heating systems through public programmes. The UK should lead by example a few months before the world will gather in Glasgow to hold [Cop26] climate talks.”

A spokesperson for the Department for Business, Energy and Industrial Strategy said: “While we remain committed to transitioning away from gas boilers over the next 15 years, we make no apology for supporting low-income households in the short term to replace a limited number of the most inefficient gas boilers, thereby cutting energy bills and CO₂ emissions. The majority of the 3.3m measures installed under the energy company obligation so far are insulation measures, and we expect that to continue in the future.”