Size of furnaces is measured in BTUs or British thermal units. The necessary BTUs for a forced air gas furnace will depend on the size of the home to be heated and the air movement in the home. Ceiling height and insulation in the home will also affect the size of the furnace. A professional should determine the size necessary for a home. BTUs range from about 70,000 to about 110,000 BTUs. The more power, the more expensive the unit. The basic furnace at 70,000 BTUs in 2010 was about $850 for the furnace only, while a 110,000 BTU was about $950.
High efficiency condensing gas furnaces are the most efficient type of furnace. They are also less expensive to install because there is no need for a chimney to vent combustion gas to the exterior of the home. Two-stage furnaces are also highly efficient. They run at full force when the weather is coldest, but most of the time run at 70 percent capacity for a savings in energy consumption. In 2010, two-stage furnaces ranged from $1,734 for a 70,000 BTU to about $2,131 for a 115,000 BTU. A single stage 70,000 BTU ran about $1,544, and a 100,000 BTU was around $1,799. Both types operate at 95 percent efficiency.
The last factor that affects price is the installation. This will vary with the complexity of the install, the contractor doing the work, and whether or not an air conditioning unit is included in the installation package. Expect to pay 1.5 times the cost of the furnace for installation.