The method described here is based on a Standard Table of Seasona1 Efficiencies and the following experimental data, which represent the furnace or boiler under test:

• The conventional, ANSI efficiency measured in the lab tinder steady state conditions
• Two (dynamic) flue temperatures measured at 5 min. after flame-on and at 5 min. after flame-off, and
• A quantitative description of energy saving features.

The inputs are sufficient to locate or interpolate the appropriate Seasonal Cost Efficiency in the Table. Cost Efficiency (or Cost COP) is defined as the ratio between total output energy (in terms of its worth on a current $/BTU or $/kWh scale, respectively) and the total cost of the input energy. This definition of efficiency is necessary in order to avoid inconsistencies with total operating cost. It also makes possible operating cost comparisons among different types of heating systems; including hybrid heat pumps. Although it is a new concept, System Cost Efficiency is identical to conventionally defined system efficiencies for systems consuming only one type of fuel.