According to the Chicago Tribune, FHA can now offer up to 5% larger mortgage amounts to people who plan to make energy efficiency improvements to the home. On a $250,000 house, this is over $12,000, or enough to replace the regular water heater with a solar hot water version.
Part of the House’s cap and trade bill also includes provisions to establish location efficient mortgages, raising the qualifying income threshold if the property is close to transit or employment centers. If you spend less on transportation (both in fuel costs and maybe even automobile costs), you can buy more house. This is intended to have the added benefit of reducing greenhouse gas pollution.