Thermal efficiency is mathematically defined as the ratio of boiler output to boiler input. In order to understand the limitations of ‘thermal efficiency,’ we must first consider exactly what the term means. Bandied about in advertisements and marketing promotions, thermal efficiency is often incorrectly considered synonymous with “energy efficiency.” While thermal efficiency does have a tremendous impact on energy efficiency, it does not fully account for all the factors that ultimately determine the energy efficiency of the entire system. One of the most commonly encountered terms describing boiler or hot water heater performance, “thermal efficiency” is also arguably the most commonly misunderstood. Our discussion starts with thermal efficiency. This technical paper will explain the advantages of modulation, demonstrating conclusively, that modulation is the firing configuration of choice. By combining half-truths with a little marketing, they’ve won the minds of a few engineers and contractors. Despite volumes of case studies to the contrary, these companies have even gone so far as to claim that modulation wastes energy. Only recently has modulation come under attack by one or two upstart companies that apparently lack the engineering expertise to develop a successful modulating design. For decades, reputable boiler and hot water heater manufacturers have been producing gas fired appliances that capitalize on the advantages of modulating firing.

Ebc12 modulating draft control