What type of furnace utilizes a fan to force air through ducts?

A forced warm-air furnace is specifically designed to use a fan for the distribution of heated air through a system of ducts. This type of furnace generates heat and then relies on a blower fan to push that warm air throughout the building, making it an efficient method of heating a space.

In contrast, a gravity warm-air furnace depends on natural convection to circulate warm air without the use of a fan, relying instead on the natural rise of heated air. An electric furnace generates heat using electrical elements and may use a fan for distribution, but the specific terminology for a furnace that utilizes a fan primarily refers to forced warm-air systems. An oil furnace may also be a type of forced warm-air furnace if it uses a fan, but the term "forced warm-air furnace" encompasses a broader range of possible fuel types and emphasizes the forced air aspect. Therefore, the best answer to the question is the one that directly describes the use of a fan to push air through ducts.