From Power Engineering
The phrase "boiler upgrade" might call to mind images of increasing a boiler's efficiency or output. While that does make up a portion of the current boiler upgrade work, the main drivers for boiler upgrades currently are very different.
"The primary influence would probably be the cost of fuel, because that's always the long-term cost of a boiler system," said American Boiler Manufacturers Association President Randy Rawson. "For those users that are fueled by oil, they're looking to go to natural gas if they can in their localities. For those fueled by coal, they're probably looking to do the same thing."