Which? has called on the government to ensure the Green Deal leads to real savings on energy prices.
The organisation has suggested four ways in which the coalition can do this.
It claims there mustn't be any harsh penalties for people who want to repay their Green Deal earlier, while any quotes for loans have to be comparable.
Which? also warns the scheme can't be a licence to mis-sell and the Energy Company Obligation has to be cost effective for everyone.
Executive director of the consumer watchdog Richard Lloyd said: "There must be fairer terms of finance, stronger protection on sales and marketing practices and more accurate savings estimates."
The Green Deal will be launched this autumn and is being introduced under the Energy Act 2011.
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