What is boiler load?

Boiler load is the total "work" performed by the boiler. In residential application the boiler load usually refers to the total heat lost in a home on the coldest day of the year and is measured in the USA by British Thermal Units per hour.

To find the load the accepted practice is to use the "Manual 'J' method. Appropriate software and some experience is necessary to gain meaningful results and proper size a boiler to the load.

Boilers that are oversize use more fuel, suffer component failures and can create discomfort by lowering the average water temperature. Boilers sized below the load will not satisfy the thermostat on the coldest days of the year.