Industries and power plants use boilers extensively as a steam generating system. Boilers use a substantial amount of the world's energy supply. Much more fossil fuel can be saved and CO2 emissions can be decreased with even a slight increase in boiler efficiency. This paper outlines the energy consumption of boilers, the methods used to assess their energy efficiency, the losses that have occurred and their reasons, the role that maintenance activities play in preventing heat loss, the quantity of waste energy recovered, and the methods of raising public awareness of energy consumption. On the aforementioned subjects, the most recent published literature has been examined and reported. This includes journal articles, PhD and MSc theses, conference proceedings, reports, and online resources. The high temperature flue gas or boiler exhaust is discovered to be a significant source of energy loss. Also, for a variety of reasons, there are certain other inevitable losses. However, waste heat may be captured and used to provide power, heat, refrigeration effect, and other useful forms of energy utilizing a variety of methods. By doing planned maintenance, one may increase a boiler's efficiency and keep it operating at peak performance. Staff members must regularly participate in education programs and seminars aimed at raising knowledge about energy consumption. As a result, they will be better able to comprehend the significance of the energy utilized in the boiler system and the effects of their activities on it.