Outdoor Boiler Furnaces are used as an alternative heat source that works in conjunction with your existing heat source. As an outdoor wood-burning unit transfers hot water into your home for heating. Boilers provide whole-home heat at a fraction of the cost of electricity, oil or gas. Boiler furnaces are ideal for heating houses, shops, greenhouses, pools, hot tubs, garages, sheds and domestic water. Adding a boiler is easy because it connects directly into your existing heating system leaving any wood mess outdoors.