What type of furnaces and boilers require combustion air for operation?

Fuel-fired furnaces and boilers necessitate combustion air for proper operation because they rely on the burning of fuel, such as natural gas, propane, oil, or other hydrocarbons, to generate heat. During this combustion process, oxygen from the air is required to facilitate the chemical reaction that produces heat. A sufficient supply of combustion air ensures efficient operation, optimal fuel utilization, and reduced emissions.

In contrast, electric furnaces and boilers do not require combustion air since they generate heat through electrical resistance rather than burning fuel. Solar furnaces and boilers harness energy from the sun to heat water or air, eliminating the need for combustion processes and the associated air supply. High-efficiency furnaces and boilers, while often designed to use fuel more effectively and to minimize emissions, still fall under the category of fuel-fired systems, as they continue to rely on combustion air to function correctly.

Therefore, the necessity for combustion air is exclusive to fuel-fired systems, making this choice the accurate one in this context.