Published efficiency testing consists of operating the appliance over a specific period of time, measuring the temperatures of the inlet and outlet water, and calculating the BTU absorbed by the water. Simple enough? Maybe it's not as simple sounds.
There are test conditions to be considered and these conditions turn out to be the major determinate of a product's published energy efficiency. The following is a quick summary of test conditions that have a significant effect on published energy efficiency
Those familiar with water heater and water boiler installations will immediately notice that conventional NON-condensing equipment will not be installed to operate under any of these conditions. Conventional OFF/ON NON-condensing equipment will be used on loads that are less than full BTU input (therefore requiring cycling) and applications where the feed water temperature will be 140°F or so rather 80°.
An obvious question arises. If equipment will not be operated under the conditions of its published efficiency test, of what relevance is the efficiency testing?