If you are going to get serious about fan work, in addition to IR-gun, accurate thermometers, and electrical multimeter,
you are going to need to measure tiny pressure differences with a mini digital manometer.
After reading Amazon reviews I took a chance on a $36 HT-1890 “no name” Chinese unit and it has worked pretty well. These also can be valuable evaluating the low pressures of exhaust systems.

Years ago we had to use inclined tube mechanical manometers, some of which were 6 foot long and had to be perfectly level to read accurately.