A furnace is a major unit found in the vast majority of homes across America. They are used to heat rooms when outdoor temperatures drop below a natural room temperature. Forces air furnaces are the most common type of modern furnace. This page contains information about different types of furnaces including commercial applications as well as residential.

In British English, the word "furnace" is used to refer solely to industrial furnaces. Industrial furnaces can have a number of uses, including smelting, in chemical plants and in oil refineries.

Many modern homes are heated with a forced air heating system. This means that the furnace is hooked up to duck work with a blower forcing hot air into most rooms in the home. Air conditioners can also be hooked up to the duct work, making for a climate control system that can keep you warm in the winter and cool in the summer.