In most cases, newer, more efficient furnaces can replace older units. Homeowners looking for better efficiency can also consider boilers, which offer better efficiency but, in most cases, high installation costs due to the need for new pipes and radiators.
While boilers offer better efficiency than furnaces, the savings can be minimal for small- and medium-sized homes. Upgrading to a newer furnace, however, can lead to substantial savings with a small investment if the existing vents and other infrastructure can be reused. Some wall-mounted furnaces offer a reasonable compromise between cost and efficiency if only a single room in a home needs additional heating.