What is generally one of the two broad categories of furnace heating systems?

A gravity warm-air furnace is one of the two broad categories of furnace heating systems, primarily distinguished by its method of heating and distribution. This type of furnace relies on natural convection to circulate warm air throughout a space. As the air is heated within the unit, it becomes less dense and rises, creating a natural flow that pulls cooler air into the system for heating. Gravity systems have been common in older homes and are often recognized for their simplicity and reliance on the natural principles of airflow.

The other broad category typically recognized alongside gravity warm-air furnaces is forced-air furnaces, which utilize fans or blowers to circulate heated air. Understanding the distinction between these types is essential for home inspectors, as it can influence the inspection process, maintenance considerations, and potential energy efficiency concerns. While electric, solar, and hydronic systems also serve to heat space, they fall outside of the broad classifications centered around furnace types used traditionally in residential settings.