A furnace uses energy to produce and deliver heat. The more heat it can deliver with a given amount of energy, the better: This is the efficiency of the Furnace. To run the blowers that circulate heat you want a furnace that is efficient while using minimal energy.
Furnace fuel efficiency ratings
The measurement for furnace fuel efficiency is called an Annual Fuel Utilization Efficiency (AFUE) rating. To find your rating look for a yellow “EnergyGuide” label that’s required by the Federal Trade Commission. AFUE ratings run from the 80 percent minimum to 98.5 percent. The meaning of this percentage is very simple: This is the ratio of the furnace’s annual fossil fuel that is converted into usable heat.
If the AFUE is higher than 90 percent it’s considered “high efficiency” and models with an 80 percent to 83 percent AFUE as “mid efficiency.”
Rise in heating cost.
Buzzing, clicking, or humming sounds coming from the furnace
Rust, soot, or moisture are present around your furnace
Leaks of any kind
Decrease in energy efficiency