Which of the following is a factor that can affect boiler efficiency?

Boiler efficiency is influenced by a variety of factors, and each of the elements mentioned plays a significant role.

Ambient temperature affects how well a boiler can maintain desired temperatures; if the outside air is significantly colder, the boiler has to work harder to keep up, which can reduce efficiency.

The quality of water used is crucial because impurities such as minerals can form scale inside the boiler. This buildup reduces heat transfer efficiency, meaning more fuel is required to achieve the same output. It can also lead to operational issues and increased maintenance costs.

The frequency of usage is another important consideration. Boilers that operate continuously tend to be more efficient than those that cycle on and off frequently, as constant operation allows for better temperature maintenance and fuel utilization.

Since all these factors—ambient temperature, water quality, and frequency of usage—impact the boiler's performance and energy consumption, a comprehensive view recognizes that they collectively determine overall boiler efficiency. This makes the answer encompassing all of them the most accurate choice.