Copyright Goodheart-Willcox Co., Inc. 42 Hydronic Heating: Systems and Applications Goodheart-Willcox Publisher Figure 3-1. Hot water boilers are available in many different configurations. A—A medium-efficiency industrial boiler. B—A wall-hung, high-efficiency boiler. C—A floor-standing, high-efficiency boiler. water temperature of up to 180°F. Most low-pressure boilers are used for residential and commercial comfort heating applications, with the majority of residential boilers having an input rating of below 300,000 Btu/hr. The input rating is the measurement of the amount of fuel the boiler will burn, stated in either Btu/hr or Mbh (1000 Btu/hr). Low-pressure boiler ratings are dictated and tested according to the American Society of Mechanical Engineers (ASME) code requirements, and every boiler is required to list these rat- ings on its nameplate, Figure 3-2. 3.1.2 Medium-Pressure Boilers Medium-pressure boilers have an operating pressure range of 160 to 300 psi and an operating water temperature of between 250°F and 350°F. These boilers are typically used for manufacturing process applications such as for food, paper, and chemicals. They may also be used for the dry cleaning and laundromat industries. 3.1.3 High-Pressure Boilers High-pressure boilers have an operating pressure above 300 psi and typically have an operating water temperature above 350°F. Applications for high-pressure boilers include metal plating and anodizing tanks, laminating processes, food processing, plastic manufacturing, and parts washing systems. One advantage of high-pressure boilers is the lower initial equipment cost as compared to high-pressure steam applications. In addition, a high-pressure hot water boiler can save on maintenance costs as compared to steam due to the elimination of steam trap discharge losses and boiler water treatment. They have virtually no make-up water costs. Furthermore, pip- ing distribution systems are easier to install and have fewer complications than do steam heating systems. Lubos Chlubny/Shutterstock.com A B C Goodheart-Willcox Publisher Goodheart-Willcox Publisher Figure 3-2. An example of a boiler’s rating plate, or nameplate, with an input rating of 45,000 Btu/hr.