What type of furnace is likely to have an AFUE rating categorized as low-efficiency?

An oil furnace is likely to have an Annual Fuel Utilization Efficiency (AFUE) rating categorized as low-efficiency compared to other types of furnaces. AFUE is a measure of how efficiently a furnace converts fuel into heat over the course of a year.

Historically, many oil furnaces are older models, which tend to have AFUE ratings significantly lower than newer gas, propane, or electric furnaces. While advances in technology have led to the development of more efficient oil furnaces, many existing units still operate at lower efficiencies.

In contrast, modern gas and propane furnaces often achieve higher AFUE ratings due to their design and combustion technology, which allows for better fuel utilization. Electric furnaces generally provide an efficient heating method, but they operate differently and do not use AFUE as a measure in the same way.

This context helps clarify why oil furnaces, particularly older models, are considered to have low-efficiency ratings relative to other types of furnaces.