It is important to understand that in a commercial application (can also apply to residential boiler applications) is going to consume a large amount of the energy budget therefore it is important to track efficiencies because a slight drop in the efficiency can cause a sharp increase in the energy costs. Understanding that, we all know it is important to have good preventive maintenance practices and regular system tune-ups including preventive maintenance practices. When we talk about efficiency we talk about two related types of efficiencies and both can have an impact on the energy budget. There is efficiency and there is combustion efficiency. A decrease in combustion efficiency will decrease efficiency but not necessarily vice versa.