Prime Minister John Key has announced that all the main trading banks have agreed to join the government's insulation and heating scheme, and all have agreed to waive their fees for top-up loans homeowners get as part of insulation retrofits.

Prime Minister John Key launched the scheme in Christchurch on Thursday along with Energy and Resources Minister, Gerry Brownlee, and Green Party Energy spokesperson, Jeanette Fitzsimons.

The scheme will officially be called "Warm Up New Zealand: Heat Smart".

The government announced in the budget it was spending $323 million over four years to retrofit 180,000 homes with insulation and clean-heating devices.

The scheme provides government grants of $1,300 towards a third of the cost of insulation and a $500 grant for clean heaters.

It starts on July 1 and will be run by the Energy Efficiency and Conservation Authority.

Thirty providers are already on board, and EECA have begun to take registrations of new providers, who are expected to be operational within three months.

In the first year, 27,000 homes are to be retrofitted, building to more than 60,000 in the fourth year.