Central Boiler manufactures and distributes the Classic, Classic Edge and E-Classic outdoor wood furnaces, the Maxim outdoor wood pellet and corn furnace and the Forge outdoor coal furnace. These outdoor hydronic heaters can heat multiple buildings, hot tubs, pools, greenhouses and more. While burning a wood stove indoors can mean many problems, there is an alternative...a Central Boiler outdoor furnace. Also known as an outdoor boiler or outdoor hydronic heater, an outdoor furnace eliminates the problems associated with indoor burning and allows you to get even more benefits. Central Boiler outdoor furnaces can actually improve the indoor environment, while eliminating the time-consuming chore of tending a traditional wood stove.