To assess the energy efficiency of your gas furnace, check its Annual Fuel Utilization Efficiency (AFUE) rating. This rating, typically expressed as a percentage, indicates how much fuel is converted into heat. The higher the AFUE percentage, the more efficient the furnace. Modern, high-efficiency furnaces usually have an AFUE rating of 90% or higher. Comparing your furnace's AFUE rating to the latest standards can help determine if an upgrade might be beneficial for better energy efficiency and cost savings. Regular maintenance can also ensure your furnace operates at its peak efficiency.