Commercial boilers are commonly used to heat buildings such as schools, offices, apartment buildings, and hospitals. Commercial boilers can use either gas or oil as the fuel source and generate either hot water or steam. The heated water or steam is circulated through radiators, baseboard units, or fan coils. Commercial boilers are defined as having an input of at least 300,000 Btu/h (British thermal units per hour).
DOE finalized the current standards for commercial boilers in 2009, and they took effect in 2012. Those standards were based on efficiency levels in the 2007 version of ASHRAE 90.1, which is a commercial building energy code. (The Energy Policy and Conservation Act (EPCA) requires that if the equipment efficiency levels in ASHRAE Standard 90.1 are amended, DOE must either establish amended standards for the products at the levels specified in ASHRAE 90.1 or establish more stringent standards if they would result in significant additional energy savings and are technologically feasible and economically justified.) The standards require a minimum efficiency of 77% to 84% depending on the specific type, size, and fuel. The most common type of commercial boilers—small, gas-fired, hot water boilers—must meet a minimum efficiency of 80%.
DOE issued a final rule in 2016, which would increase the minimum efficiency levels to 81% to 88%. However, the final rule has yet to be officially published in the Federal Register.
About one-quarter of all commercial floor space is heated by commercial boilers. Commercial boilers are generally used to heat buildings that have a heating and cooling system referred to as a central system, where boilers provide hot water or steam for heating and a chiller provides cold water for cooling. (In contrast, other buildings may be heated and cooled used packaged rooftop units, for example.) Much greater energy savings from commercial boilers are possible using condensing technology. Condensing boilers extract additional heat by condensing the water vapor in the flue gases. Gas-fired hot water boilers using condensing technology can reach efficiency levels as high as 99%.