What is the heat gain for an industrial sewing machine?

This question cannot be reasonably answered as written.

Before any realistic assessment of heat gain can be established for a product, the product must be specifically identified. Also, the test criterion must be established along with specific parameters that can reliably be reproduced. Operator run industrial sewing machines do not generally have enough heat gain to create any difficulties when utilized under the typical conditions. Of course there are variables. As example, if one were speaking of heat gain (rise actually) at the needle while stitching items such as plastic zippers, and concerned with melting the zipper, that is an issue. There are many, many other complex issues however and a guess could not be ventured without more information.

The motors on the typical, operator run industrial sewing machines, often one horsepower 1725 RPM internally fan cooled 110 volt motors, can have a heat gain of approx 2,000 BTU's if running continually and under a light load. Of course this answer is meaningless if this is not what you need to know, if you are using the motor in an off and on fashion, or is the fabrics being stitched are unusually heavy, etc. etc. etc. etc. etc. etc. etc. etc. etc. etc. etc. Lots of possibilities.

[I was the lead columnist with IFAI (Industrial Fabrics Association International) magazine, and considered an expert in industrial fabrics, fabrication methods, machines, processes, and designs. Ask this question providing the detail needed and perhaps I can assist]