Infrared Thermometers.. Can Cause Confusion



There are three reasons why I don’t like infrared thermometers for many HVAC tasks.

#1 – The Laser is 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 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, generally non-metallic surfaces. Metals have a low emissivity (much less than 1 generally) which means that if you are reading a pipe an infrared could read much lower than the correct temperature.

Infrared thermometers can be useful to do comparisons where 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.

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.

— Bryan

P.S. – While I don’t like infrared, I REALLY like thermal imaging. Check out these nice products from Trutech tools 



  1. Robert Gore says:

    THANK YOU! I’ve told two different bosses that swear by IR guns exactly what you’ve stated about emmisivity. They looked at me like I was crazy until I told them shoot the supply air diffuser and I’ll use my Cooper air probe. Eye opener for them!

  2. Bill Spohn says:

    Good solid info.

    Regarding point #1, better IR thermometers actually paint points on the diameter or a circular ring with the laser pointer, to show you the target area, not just a center dot.
    Even the inexpensive testo 805i smart probe IR thermometer paints a target ring.

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