A/C register temp

OK, I’m feeling pretty dumb right now. I know the drop across the coils of an a/c system should be 18-22 degrees. I inspected a couple of houses and using an infrared thermometer, I am getting a temp of 32 Degrees at the register with a room temp of 74 degrees and an outside air temp of 84 degrees.

What am I doing wrong? Wrong instrument? Should I be using a bulb Thermometer?


P.S. don’t be too hard on me, I am having a bad day.

Was this at every house or just one of them?

I use a temp gun to get a quick idea of what I’m dealing with. It all really depends on the equipment, outside temp and ductwork layout. I like to see 55-60 degrees at the register on an 80 degree day and I don’t get too technically exhaustive with my hvac inspections. Nonetheless, 32 degrees is way too cold at the register if your guns working correctly. Look for other defects

Yeah I agree, 32 is way,way too cold at a register/vent.
Temps at vents depend on distance from the unit of course.
I’ll get higher temps on the 3rd floor of course if the unit is in the basement.

Typically on the first floor I’d be happy with about upper 50’s to low 60’s at the vent.

Last one I saw that cold was significantly overcharged and oversized.


Let’s do some clarification. When you measure the temperatures at the diffuser and the return register you are not actually measuring the temperature drop across the coil. To measure that requires a measurement just before the coil and one right after the coil. Where you measure puts other variables into the equation like duck leaks and heat transmission into/out of the ducts. Additionally, those infrared devices can be misleading.

However, with all that being said the temperature drop you are recording is excessive!