Unlike many other products, boilers are not typically classified as commercial or consumer grade, although the size of large boilers makes them commercial units by default. Boilers that are too large for a home waste energy.
While large boilers operate more efficiently than small boilers, large boilers also spend more energy warming larger water volumes. If the heat stored in the water is more than what a structure needs, it is wasted. In addition, large boilers warm structures faster, which causes thermostats to stop circulating their heat more quickly. Constantly cycling a boiler on and off ends up wasting additional heat. Calculating the correct size for a boiler enables homeowners to keep their operating costs as low as possible.