This paper reports on a case study of a construction project that installed modular condensing boilers in a U.S. government office building in Sioux City, Iowa. Discussions of the energy savings benefits that were provided by condensing boilers are presented. A life-cycle cost of the modular condensing boilers is determined and is compared to installing typical modern cast-iron boilers. An estimate of the expected energy savings due to the decrease in natural gas usage attributed to the boiler installation is determined. The actual decrease in natural gas usage in the facility is determined on the heating degree-day basis. Suggestions are then made to explain the difference between the expected savings of natural gas and the actual decrease in natural gas. Finally, the simple payback for the project is determined based upon the actual energy savings and construction costs.

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