The disadvantages of two-stage gas furnaces are that they may not work well in large homes and that they have a higher initial cost than single-stage furnaces. As of 2015, two-stage gas furnaces cost about $500 more than equivalent single-stage models.
Two-stage furnaces may not work well in a large home because their low-fire heat setting may not push hot air throughout the whole house. Two-stage furnaces have high-fire, low-fire and off options, while one-stage furnaces operate as either on or off. A two-stage furnace generally operates at low-fire until the weather is very cold and high-fire is needed. The high-fire setting is generally used about 25 percent of the time. One-stage furnaces utilize their full power when in use, regardless of the outside weather.
Single-stage furnaces are the traditional home furnace type. Two-stage furnaces, with their more advanced technology, are a contemporary development.
Individuals may prefer two-stage furnaces for their improved energy efficiency, quiet sound while running and the ability to keep the house at a fairly consistent temperature.
Choosing a particular type of furnace depends on the individual’s finances and needs. An individual should be well informed about the benefits and disadvantages of both single-stage and two-stage furnaces before making a decision.