Gas boilers could be banned in future but the government believes the market should drive changes to home heating systems, the cabinet minister Anne-Marie Trevelyan has said, amid criticism of the limited grants system for heat pumps.

Ministers had been under pressure to set a date to ban the installation of new gas boilers in existing homes, but on Tuesday announced the installation of low-carbon heat pumps would be encouraged with a grant system of GBP5,000 for up to 90,000 homes in England and Wales.

The grant would make the installation a similar cost to a new gas boiler, but green campaigners have said the move would expand the greener system to a minuscule proportion of homes and does not set a date for a full ban.

Speaking on Tuesday as the government launched its heat and buildings strategy, one of a number of announcements made ahead of the Cop26 summit in Glasgow, Trevelyan hinted the installation of new gas boilers would be banned in the future.

“In the short term, yes, of course this is a voluntary scheme … There will be a point at which that changes but, yes, for now that’s the case,” she told Sky News.

The international trade secretary said she believed the market would eventually change to make the greener switch more affordable. “At the moment we’re encouraging the market to drive those changes,” she told the BBC.

“What we’re seeing already is energy companies already moving into, not only providing us with energy, but encouraging their customers to shift to heat pumps and looking to find ways to help do that – your energy provider will be part of that solution.

“In 10 years’ time, we want to look back and think we’ve actually made a difference as individuals, because that’s as important as the big chunky things like offshore wind turbines and nuclear power stations.”

The full strategy is expected to be published on Tuesday and will include measures 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.

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.”

Under the plans, which the minister said would 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 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.

Ed Miliband, the shadow business secretary, said it was a “meagre, unambitious and wholly inadequate response”.

He added: “Families up and down the country desperately needed Labour’s 10-year plan investing GBP6bn a year for home insulation and zero carbon heating to cut bills by GBP400 per year, improve our energy security, create jobs and reduce carbon emissions.”