If you are in the market for a new home, you might want to consider an Energy Efficient Mortgage (EEM). Many lenders are now offering EEMs which will lend buyers extra money in order to make efficiency upgrades when making a home purchase. Whether you are retrofitting an older home with efficient upgrades or putting the newest technology into a new home, efficiency upgrades will often save you more over the long run than they will cost up front. If you amortize out the cost of a new furnace or AC system over the course of 30 years, you may be paying an extra $20/month and your savings could amount to double that. It is almost a no brainer.
In order to qualify, a home typically needs a certified energy audit. The audit will point out cost effective areas of improvement that will provide a positive return over time. In the case of a home that is already efficient, the audit will prove that the home is already efficient and this will potentially enable the lender to stretch the debt to income qualifying ratio.
US DOE -- Energy Efficiency & Renewable Energy - Financing an Energy Efficient Home
Mother Earth Living - Energy Efficient Mortages Make Home Improvement Affordable