Ministers have unveiled plans for GBP5,000 grants to allow people to install home heat pumps and other low-carbon boiler replacements as part of a wider heat and buildings strategy that some campaigners warned lacked sufficient ambition and funding.

Labour also condemned the plans as “more of Boris Johnson‘s hot air”, without sufficient substance.

Details for the scheme, to be formally set out on Tuesday alongside the government’s net-zero strategy, include GBP450m committed towards grants to replace boilers, with a pledge that the fund will mean heat pumps should cost no more than boilers to install or run.

More widely, the heat and buildings strategy contains a commitment to funding totalling GBP3.9bn to decarbonise buildings and how they are heated, with a confirmed 2035 target for all new heating systems in UK homes to be energy-efficient.

With the crucial Cop26 climate summit in Glasgow starting in a fortnight, the business and energy secretary, Kwasi Kwarteng, said recent gas price rises “have highlighted the need to double down on our efforts to reduce Britain’s reliance on fossil fuels and move away from gas boilers over the coming decade”.

He said: “As the technology improves and costs plummet over the next decade, we expect low-carbon heating systems will become the obvious, affordable choice for consumers.”

However, some environmental groups said more urgent action was needed. Caroline Jones, of Greenpeace UK, said efforts to decarbonise housing were being hampered by “unambitious policies and inadequate funding”. She said: “More money must be provided to rapidly increase the number of homeowners switching to heat pumps over the next few years, with full costs covered for families on low incomes.

“A clearer signal would have been a phase-out of new boilers before 2035. And all of this must be delivered with a fully funded, nationwide programme to insulate our homes at a scale and speed that the government hasn’t fully grasped.”

Jan Rosenow, European programme director for the Regulatory Assistance Project, a clean-energy NGO, said there were “many positive elements” in the strategy, with the ban on new fossil heating systems being a world first and a useful signal ahead of Cop26.

But he added: “Providing grants for installing heat pumps is essential as they are more expensive than gas boilers. But the level of funding is too low. Under the plans, only 30,000 homes would be able to benefit from the government grant, just enough to support current installation levels. Given that the target is to install 600,000 heat pumps per year, this is clearly not enough.”

The shadow business and energy secretary, Ed Miliband, said: “As millions of families face an energy and cost of living crisis, this is a meagre, unambitious and wholly inadequate response. People can’t warm their homes with yet more of Boris Johnson’s hot air, but that is all that is on offer.”

Under the plans, which the minister says will support up to 240,000 jobs by 2035, the GBP5,000 grants will be available from April next year, and should eliminate any price differential for heat pumps or similar systems. The plan suggests that, as the market expands, the price for such systems should drop by between a quarter and a half by 2025.

The wider GBP3.9bn of funding for greening homes will be targeted through a series of existing schemes, with others aimed at public buildings.