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Understanding energy-efficiency ratings

What to know about efficiency before you buy a new natural gas appliance

When you're in the process of buying a new natural gas water heater or furnace, you'll see energy-efficiency ratings tied to different makes and models. And because water and space heating make up a large chunk of your monthly energy bills, we want you to know exactly what each of those means so you can make the right choice for the size of your home and for your family. 

Breaking it down: AFUE and UEF ratings to help you understand energy efficiency

  • AFUE stands for Annual Fuel Utilization Efficiency and measures how efficiently your furnace uses fuel. 
  • UEF is a newly developed metric for water heater energy savings and stands for Uniform Energy Factor. UEF ratings assign water heaters into one of four usage categories and then provide information on performance based on that category of use.

The higher the rating, the lower your bills

Despite the differences between AFUE and UEF, the easiest thing to remember is that the higher the rating, the less energy the appliances uses. And less energy means lower energy bills - and that's always a good thing.


Adding it up in dollars and cents

When you're shopping for your new natural gas appliances, look for the Energy Star label. Energy Star is a program run by the U.S. Environmental Protection Agency and the U.S. Department of Energy that promotes energy efficiency. For example, if you're looking at a furnace labeled at 80% AFUE, that means for every dollar you spend on energy, 80 cents go to heating your home, while 20 cents are lost. But, if you purchase a 95% AFUE furnace, 95 cents of the same dollar go to heating your home. While a higher-rated appliance may cost more up front, you'll save more money on your energy bills each month.

Remember, the rating is just an average and doesn't reflect your personal energy usage or energy rates in your area, so it's always a good idea to check with one of Spire's energy advisors for advice.