When looking at replacement furnaces, you will likely be introduced to the idea of stages. There are three main options to choose from, depending on your budget and heating needs.

Single Stage

The most basic central heating system you can put in is likely the single stage furnace. These furnaces come with two operation options — on or off. When on, the furnace is operating at 100 percent of its available capacity.

The main benefit of a single stage furnace is cost since most cost less than tier two stage and modulating stage furnaces. Some homeowners also prefer them for simplicity since these are some of the most basic furnace designs available. The drawbacks are that the furnace is always running at peak capacity, which can cost more in both energy use and energy costs.

Two Stage

A two stage furnace has two operation levels, the 100 percent of a single stage furnace plus a second level that is typically between 50 and 75 percent of the furnace's capacity to heat. 

The benefit is obvious -- by running at a lower capacity with extreme heating isn't necessary, such as on a crisp but not freezing fall day, your energy costs will be less. Further, your furnace will also be working at a lower capacity, which often means less wear and tear on the heating unit itself. The result is you save money on both energy costs and maintenance, and your home isn't subjected to overheating.

Modulating Stages

The only thing better than two stages are more stages. A modulating furnace has three or more stages, typically allowing options below the 50 percent capacity mark. The furnace will switch between the various stages as needed, sometimes during the same heating cycle. The result is even more energy and cost savings.

A modulating stage system is usually considered the top tier in furnace operation. Allowing minute modulation of heat output during the cycle leads to more even heating throughout the home. For example, if the second floor tends to heat rapidly but it takes longer for the lower level of your home to heat, then the furnace will switch to a lower output stage once the top floor reaches the desired temperature. This allows heat to spread throughout the home as needed, instead of either overheating the home or cutting off before every room is the desired temperature. 

Contact a heating service if you want more information on furnace types and heating options.