What are four factors that determine the efficiency of a furnace?

The efficiency of a furnace is determined by several factors, including:

1. Fuel Type: Different fuels have varying energy contents and combustion efficiencies, impacting overall performance.
2. Insulation: Proper insulation minimizes heat loss, ensuring that more energy is used for heating rather than escaping.
3. Burner Design: The design and maintenance of the burner affect how completely fuel is combusted, influencing efficiency.
4. Air-Fuel Ratio: An optimal air-fuel mixture is crucial for complete combustion; too much or too little air can lead to wasted fuel and reduced efficiency.