The package boiler and burner market is evolving to adapt to new environmental regulations. Current environmental regulation trends strive for lower NOx and carbon monoxide (CO) emissions from fired package equipment. As a result, older boilers are either replaced with new package boilers or retrofitted to install new low-NOx burners (LNB) or ultra-low-NOx burners (ULNB). Whether a facility chooses to replace existing boilers or burners to comply with new environmental regulations, end users must consider the construction of the boiler to ensure the CO emission requirements can be achieved.