Delta T in HVAC! 💪 #hvac

Added: 2026-05-16

[00:00:00]Hi, I'm Ryan, director and dean of HVAC University, and this is your mechanical minute. Today, we're talking about delta T in HVAC. At its core, delta T simply is a temperature difference across a piece of equipment, whether it's air or water. That simple number tells us a lot about how effectively a system is actually moving heat. Across the furnace, a proper temperature rise confirms a system transferring heat safely. Too high and the risk of overheating the heat exchanger, too low and you're likely dealing with air flow issues or poor combustion efficiency.

[00:00:34]The basic formula that we have is BTUs over 1.8 atmospheric pressure times delta T, which our delta T is 45°.

[00:00:45]Remember, CFM means cubic feet per minute, how fast the air is moving. BTUs is the amount of heat that the unit is producing, British thermal unit. In cooling, we use the return minus the supply in order to get our temperature drop. The nameplate on a unit tells us temperature rise, high fire, low fire, but it also tells us the BTUs of the unit. To get the delta T, we take the temperature of the supply minus the return, that is our temperature rise.

[00:01:15]Equation comes out to be 1,428 CFM. In elevation, we change the atmospheric pressure to 0.89 times our delta T, which is still 45°. Supply minus the return, there's our temperature rise, 1,750 CFM. So, delta T isn't just a measurement, it's a gateway to understanding the actual system.

[00:01:37]Instead of guessing, delta T gives us a fast, reliable diagnostic. At the end of the day, delta T in HVAC is the way to go. Measure it and be confident. I'm Ryan with your mechanical minute, and this is HVAC University.