The Prime Minister says the overwhelming take-up of the Government's Heat Smart programme is a welcome surprise.
In just the first year, more than 50,000 homes have been retrofitted under the scheme, which subsidises home insulation or improved heating.
John Key says the Government had expected only about half that number, so funding had to be brought forward.
The Government has committed almost $350 million to the programme over four years, though that could be boosted, Mr Key says, if the large demand for the service continues.
He says the Government is well on track to meeting its target of insulating at least 188,000 homes by 2013.