Natural gas, propane or heating oil is burned to warm a reservoir of water that is distributed, via pumps or by converting it to steam, throughout the structure. Commercial boilers are defined as those with a heat input rate greater than 300,000 BTUs per hour.
In principle, both residential and commercial boilers operate similarly. The water in the boiler is used to store and distribute the heat generated. Steam boilers convert the water to steam, which spreads through pipes automatically and condenses as it loses heat, after which it drains back to the boiler. Hot water boilers, which rely on pumps to send the water, offer better efficiency but use energy to transfer water.
Despite the superior efficiency of hot water boilers, many older buildings have the piping and radiators needed for steam boilers. The cost of replacing this equipment can be prohibitively expensive, and the efficiency gains of switching to a hot water boiler can be fairly small, especially in larger buildings. Because of this, steam boilers are still popular in older buildings.
Commercial boilers often have more sophisticated interfaces than residential units. Heating costs in large buildings are generally high, and even small efficiency increases can lead to significant savings over time. In addition, commercial HVAC equipment is often placed in a large room, which gives technicians plenty of space to perform repairs and install new equipment if needed.