What is a common characteristic of furnaces in residential settings?

The correct answer highlights that furnaces in residential settings typically operate using gas or electricity as their primary energy sources. This characteristic is fundamental because it defines the most common types of furnaces found in homes, such as gas furnaces that combust natural gas or propane to generate heat and electric furnaces that convert electrical energy into heat.

Furnaces are designed to efficiently convert fuel into heat and distribute this heat throughout the home via ducts or other means. Understanding this characteristic is crucial for homeowners and energy raters alike as it relates to energy efficiency, operational costs, and understanding the impact on home energy ratings.

While other options may represent heating systems or concepts, they do not accurately describe the general functionality and common operation of residential furnaces, which is why recognizing gas or electricity as the primary heating sources is key.