### Question
How is the term efficiency descriptor defined?


### Answer
The term **efficiency descriptor** is defined in *42 U.S.C. § 6291* as the following:

> the ratio of the useful output to the total energy input, determined using the test procedures prescribed under section 6293 of this title and expressed for the following products in the following terms:


(A) For furnaces and direct heating equipment, annual fuel utilization efficiency

#### Citation:
  - *42 U.S.C. § 6291*
  - Heading: **CHAPTER 77-ENERGY CONSERVATION > SUBCHAPTER III-IMPROVING ENERGY EFFICIENCY > Part A-Energy Conservation Program for Consumer Products Other Than Automobiles**

