The most efficient boiler for any particular operation depends on the process being run.
For heating a building, a boiler of around 82-87% efficiency is recommended to achieve the maximum energy savings while meeting current NOx requirements.
For operations that produce cooler return water, a condensing boiler is recommended. The cooler the return water, the more efficient the boiler system can get. Most condensing boilers achieve around 92-94% efficiency.
Newer-design firetube boilers that feature XID tubes combined with economizers are recommended for process and hospitals where steam is used. The XID tubes help increase boiler heat transfer to 84 – 85%, and the economizers can help recover heat on the back end and increase the boiler efficiency even higher with an outside heat requirement.