Boilers can fire a wide range of fuels, including natural gas, fuel oil, and solid fuel.
Burners that burn fuel oil need steam as an atomizing medium. The additional steam in combination with the higher excess air required to burn fuel oil increases the fuel
requirement for oil burning. Many older burners have low fuel efficiency and high NOx
production. Over the years, due to regulation, the burners in many boilers have been
replaced with low-NOx burners with high combustion efficiency.