PG&E offers energy efficiency rebates for customers who install high efficiency furnaces. For furnaces that 94 percent efficient and higher, up to 96 percent, are eligible for a $150 rebate while furnaces with a 96 percent efficiency rating or higher qualify for a $250 rebate. If the furnaces have a built-in VSM, those rebates are bumped up to $200 and $300 respectively.

The federal government is also offering a federal energy efficiency tax credit through 2010 for high efficiency furnace installations. To qualify, you'll need to install a 95 percent efficient furnace or better in your primary U.S. home. The credit is designed to cover 30 percent up to $1,500 of the cost of the furnace. Other eligible upgrades include insulation, air sealing, water heaters and more.