A residential boiler is designed to generate adequate heat for a typical residential building. In order to serve the heating requirements of much larger buildings like warehouses, office buildings, and retail outlets, commercial boilers are typically much larger, and more expensive. Boilers are often rated in MBHs or BTUs. A BTU is the amount of energy required to raise the temperature of one pound of water one degree Fahrenheit. MBH is one thousand BTU. A commercial boiler can be rated up to 2500 MBH or even more, while a household boiler may only be rated between 30 and 300 MBH.