Changes to the Energy Company Obligation (ECO) will make sure energy companies give support to people struggling to meet their heating bills, it said.
The measures came into force on 1 April with plans to extend the scheme from April 2017 to September 2018 also confirmed.
Consumer minister Margot James said: "The big energy firms already have to help households save gas and electricity bills, by improving homes so they are easier and cheaper to keep warm.
"We're strengthening this obligation today and making sure they prioritise low income households as part of our plan to insulate 1 million homes by 2020."
The reforms, which were consulted on last year, would simplify the scheme, said Ms James.
Energy companies will be required to provide struggling households with energy efficiency measures to make their homes warmer and bring their bills down.
As well as an increased focus on low income and vulnerable homes, eligibility will be extended to social housing tenants in EPC bands E, F and G.
Local authorities will also be able to help match people with energy suppliers.
Suppliers will also be required to install a minimum 21,000 solid wall insulations per year, up from the earlier proposal of 17,000.
Specific protection for energy efficiency measures in rural areas will continue.
This protection requires that 15% of suppliers' Carbon Emissions Reduction Obligation be delivered in rural homes.
The government says ECO has proved "very effective" with some 2.2m measures installed in around 1.7m properties between 2013 and the end of January 2017.