How to replace your furnace

Go with high-efficiency?

A furnace can generate a certain amount of heat per hour. This number is expressed in British thermal units (BTUs). The higher the number, the larger the home the furnace can heat.

Furnace efficiency is expressed as average fuel use efficiency (AFUE), which measures the percentage of input BTUs the furnace can convert into output BTUs, or heat.

Today’s furnaces have an 80% to 98% AFUE, depending on the model.

Andrew Webb, business development manager of AC Pro in Fontana, California, says it doesn’t always make sense to buy the most efficient furnace from a cost versus savings standpoint.

“Here in Southern California, we very rarely use our gas furnace, and we recommend most homeowners to purchase an 80% efficient furnace, as the cost difference won't be made up if purchasing a higher-efficiency furnace,” he says.

If you live in the Northern or Northeastern United States and use your furnace for five-plus months per year, however, purchasing a 95% to 98% efficient furnace can pay for itself over the first five to 10 years, Webb says.