In order to maintain an efficient furnace, annual professional maintenance is not a suggestion—it's a requirement. AFUE will decline over the years due to ductwork leaks and inefficiencies, dirty furnace components, loose and damaged parts, and clogged air filters.
This is an extremely important part. If it's not working, you won't receive any heat. Heat exchanger can also be dangerous if they develop any leaks or cracks.
Learn more furnace safety and efficiency tips. Find out if you should invest in a new furnace.
Older, low-efficiency furnaces have an AFUE rating between 50% and 70%. Mid-range efficiency furnaces around 80% to 85%, while high-efficiency furnaces have AFUE rating above 90%, sometimes as high as 98.5%.