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Infrared Thermometers Can Cause Confusion
There are three reasons why I don't like infrared thermometers for many HVAC tasks.
#1 – The laser can be misleading
The laser dot is just a point of reference, not an exact point where it is reading. Often the thermometer will read lower, higher, or over a MUCH wider area. Unless you are right up on what you are measuring, you can't be sure the result you are getting is correct.
#2 – They only read surfaces
An infrared reads surface temp only, not air temp. This is not necessarily a problem, but “shooting a vent” is not the same as measuring the air temperature coming out of it.
#3 – They can be VERY inaccurate
Basic infrared thermometers are only accurate on a surface that has high “emissivity” of near 1.0. These are usually darker, less reflective, and generally non-metallic surfaces. Metals have a low emissivity (much less than 1, generally; you can read more about emissivity in this article). That means that if you are reading a pipe, an infrared thermometer could read much lower than the correct temperature.
Infrared thermometers can be useful for making comparisons when reading the correct temperature is less important than comparing one spot to another, such as looking for hot spots in a panel or checking a zone to see if a damper is open. You have to know how to use them correctly and understand what you're looking for, but they can be useful. (I actually made a video showing how to use the Refco LP-88 infrared thermometer HERE.)
So long as you use the right tool for the job, you should be fine, but in general…
I don't like techs using infrared thermometers for most tasks.
P.S. – While I don't generally like infrared thermometers, I REALLY like thermal imaging. I used a thermal imaging camera to help diagnose a problem with NBA player Bo Outlaw's HVAC system; you can watch that process HERE. I also recommend checking out these nice products from Trutech tools.