Central Boiler outdoor furnaces’ energy efficient designs maximize the combustion and heat transfer process for better heat delivery. In other words, Central Boiler outdoor furnaces burn more completely and efficiently, and transfer more of the heat generated to your home. Current owners of Central Boiler outdoor furnaces report that they are using up to 25% to 70% less wood compared to traditional wood furnaces or other brands of outdoor wood furnaces. Indoor wood stoves can be less efficient because heated indoor air used for combustion is sent out the chimney, causing cold air to be drawn into the house to replace it.