Energy engineers need a means to analyze the performance of cycling boilers in order to quantify their performance for justifying boiler replacements. That information is not available from the manufacturer because cycling efficiency is particular to the installation. The author has created a cycling efficiency model that can be used to determine operating costs and make comparisons when loads or boilers are to be changed. The model is a simple spreadsheet format which should be usable by all energy engineers. Two examples of systems the author analyzed are described to help explain its use. The model design relates to heating boilers but could be applied to boilers serving production loads. In the author's experience, most simple heating boilers could be replaced by one-fourth to one-third of their size with an increase in actual efficiency from 50 to 70 percent. Most of the nation's inventory of heating boilers are outsized. With the ability to determine cycling efficiency, it's possible to prove the low efficiency of an existing boiler and justify its replacement with something smaller.