What characterizes a two-stage boiler?

A two-stage boiler is characterized by its ability to operate at two different firing rates, which enhances its efficiency and allows for better adjustment to varying heating demands. The dual firing rates typically include a high-fire setting for maximum output and a low-fire setting that conserves energy during periods of lower heating needs. This feature helps in maintaining optimal performance and comfort while also reducing fuel consumption and greenhouse gas emissions.

In contrast, the other options do not accurately represent the characteristics associated with a two-stage boiler. For example, while some boilers may run on different fuel types, including electricity and gas, this does not define a two-stage boiler. Moreover, the idea that a two-stage boiler is limited to small applications or is designed for one-time use is not relevant. This type of boiler is commonly used for a variety of heating demands in residential and commercial settings, not restricted by application size or intended usage duration.