National Fireplace Institute (NFI) Core Knowledge 2025 – 400 Free Practice Questions to Pass the Exam

Efficiency in a heating appliance is calculated by taking the heat output and dividing it by the heat input. This ratio expresses how much of the energy supplied to the appliance is converted into useful heat for space heating or water heating. A higher efficiency means that a larger portion of the energy consumed is being utilized effectively for heating purposes, which is important for both performance and energy cost savings.

For instance, if a heating appliance has a heat input of 100 units and a heat output of 90 units, the efficiency can be calculated as 90 divided by 100, resulting in an efficiency of 90%. This metric is crucial for determining how well the appliance is functioning and can help consumers choose more effective heating solutions for their homes.

The other options do not represent the proper formula for calculating efficiency. Heat input plus heat output, or heat output minus heat input, does not yield a meaningful measure of efficiency in the context of heating appliances.