The output of a fin tube radiator, also referred to as its heating capacity or heat output, depends on several factors, including the size and design of the radiator, the temperature of the hot water or steam circulating within the tubes, the flow rate of the fluid, and the temperature difference between the radiator and the surrounding air. 

Typically, the output of a fin tube radiator is measured in British Thermal Units per hour (BTU/hr) or in watts (W). The heating capacity can vary widely depending on the specific characteristics of the radiator, but it is often expressed as a range based on standard operating conditions.

For residential fin tube radiators, the output can range from a few thousand BTU/hr for smaller units used in individual rooms to tens of thousands of BTU/hr for larger radiators used to heat entire homes or buildings.

Commercial and industrial fin tube radiators may have higher outputs to accommodate larger spaces and higher heating requirements. In such cases, the output may range from tens of thousands to hundreds of thousands of BTU/hr or more, depending on the size and application of the radiator.

It's important to note that the output of a fin tube radiator is typically specified by the manufacturer based on standardized testing conditions, so actual performance may vary depending on factors such as installation, operating conditions, and maintenance.