Zoro, Drillspot and GlobalQRC all sell small steam boilers. Steam boilers operate by converting water into steam by applying heat to it, either using a water-tube or a fire-tube design, and smaller boilers are designed for buildings with smaller square footage requiring heating.
The Web pages offering small steam boilers for sale describe such characteristics as the boiler's weight, the type of fuel used, the heating capacity in British thermal units per hour, the energy input required in BtuH, the size of the connection and the AFUE rating, which indicates the efficiency. The Advanced Thermal Hydronics gas fired boiler (model HWX-105-INT) has an AFUE rating of 0.821, for example, as of 2015. This means that the boiler converts 82.1 percent of the energy it receives into heat energy.
Other important specifications listed on the product sale page include the type of ignition, the cabinet material, the housing finish and the items included in shipping. Small steam boilers generally come with a pump, pressure relief valve and a high limit and control center. GlobalQRC offers consumers the chance to email in a competitor's price on boilers to get a chance to have GlobalQRC match that competitor's price. GlobalQRC's website also provides images of similar and complementary products.