Householders are to be offered long-term loans to help make their homes more energy efficient and cut bills under a new government scheme.
Ministers say the Green Deal, which launches on Monday, will help thousands "stay warm for less".
Under the scheme, households can use cheap loans to spend on energy-saving improvements, such as insulation and new boilers, with no upfront cost.
Campaigners said the project would "not stop fuel poverty rocketing".
The Department of Energy and Climate Change (DECC), which launched the flagship scheme, said it believed hundreds more households than expected had already signed up for assessments to join the project. It said official figures were being collated.
Earlier reports had indicated just five assessments had been carried out ahead of the launch.
Deputy Prime Minister Nick Clegg said: "The Green Deal will help thousands of homes stay warm for less. Those people will benefit from energy saving improvements - and their energy bills will fall.
"The UK green sector is a success story. It is the sixth largest in the world and has a crucial part to play in building a strong economy."'Cosier' homes
He added: "The Green Deal will support thousands of jobs, not just over the next few years, but in the long-term."
End Quote Ed Matthews Energy Bill Revolution
We call on the prime minister to use money from the carbon tax to super-insulate this country's homes"
Energy and Climate Change Secretary Edward Davey also praised the "great deal", saying: "Improve the look and feel of your home, make it cosier and at the same time save energy - what's not to like?"
The move to insulate the UK's aged housing stock is designed to save carbon emissions, keep people warm, and make energy affordable, the government said.
Anyone joining the scheme would first have their home reviewed by an independent assessor, advising on possible upgrades, costs and energy saving timescales.
Green Deal providers would then calculate quotes for the proposed work - with households free to get multiple quotes - before carrying out the changes.
Under the deal, improvements are installed at no initial cost. Instead, charges are covered with cheap loans via the not-for-profit Green Deal Finance Company, and recouped gradually over up to 25 years through customers' electricity bills.
But campaigners have warned the scheme does not go far enough.
Ed Matthews, head of fuel poverty campaign group Energy Bill Revolution, said: "The Green Deal and Energy Company Obligation will not stop fuel poverty rocketing in the face of high gas prices."
"We call on the prime minister to use money from the carbon tax to super-insulate this country's homes.
"This will provide households with five times more subsidy to insulate their homes and not add a penny more to energy bills."
"It is enough to eliminate fuel poverty and in time cut bills for everyone. It is the just and fair solution."