Delta T (Temperature Split) Calculator
Free Delta T calculator for HVAC techs. Enter return-air and supply-air temperatures to get the temperature split across the evaporator coil, with normal-range guidance.
How the Delta T calculation works
Delta T (the temperature split) is the difference between the air entering the evaporator coil (return) and the air leaving it (supply). It’s one of the fastest checks of whether an air conditioning system is moving the right amount of air across a properly performing coil.
Delta T (°F) = Return-Air Temperature − Supply-Air Temperature
Worked example
Return air measures 75°F and supply air measures 56°F:
75 − 56 = 19°F split — right in the normal cooling range.
Reading the result
A typical residential cooling split runs about 16–22°F. The “right” number within that band depends on indoor humidity — the drier the indoor air (lower wet bulb), the higher the expected split.
| Split | Likely cause |
|---|---|
| Low (under ~16°F) | Too much airflow for the load, low refrigerant charge, or a failing/iced evaporator |
| Normal (16–22°F) | Airflow and capacity reasonably matched |
| High (over ~22°F) | Too little airflow — dirty filter, restricted ducts, slow blower, or dirty coil |
Delta T is a screening check, not a charging method. Pair it with superheat, subcooling, and a real airflow (CFM) measurement before condemning a component.
How FieldPad helps in the field
Take the split here, then log it in FieldPad against the equipment and the visit. Trend it across maintenance calls, attach it to the job, and turn the diagnosis into an estimate — all on one offline-ready record that travels with the client.
Stop Re-Running These Numbers by Hand
FieldPad is the all-in-one iPhone CRM for solo HVAC techs — clients, scheduling, estimates, invoices with signatures, inventory, and equipment history. Keep your readings on the job, the client, and the equipment, all in one offline-ready app. EPA Section 608 and Subpart C compliance included.
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