Temperature Split Calculator

Enter the return air dry bulb and wet bulb to get the target temperature split across the coil, and add the supply temperature to compare. It reads California Title 24's target split table, as published from 2008 to 2022.

Units

In the return plenum, before the coil.

At the same spot, after 15 minutes of running.

Target temperature split

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Fill in the boxes above to see the answer.

Actual splitReturn minus supply
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Actual vs target
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Table cell usedReadings rounded to the nearest whole °F
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In the supply plenum, after the coil, out of sight of it.

What is temperature split?

Temperature split, also called delta T, is how much the air cools as it crosses the indoor coil: the return air temperature minus the supply air temperature. With the right airflow and a working system, the air leaves the coil a predictable number of degrees colder than it went in.

The right split depends on how humid the return air is. In humid air more of the coil's work goes into pulling out moisture, so the temperature drops less. That's why the target comes from the return dry bulb and wet bulb instead of one fixed number, and why a split well above the target is a quick sign of low airflow.

How it's calculated

Target split = Title 24 Table JA6.1-1 (2008: RA3.2-3) at (return dry bulb, return wet bulb), each rounded to the nearest whole °F
Actual split = return dry bulb − supply dry bulb
2008 installer check: actual − target within ±3°F
In °C: inputs convert to °F for the lookup, and splits convert back as differences (× 5/9)

Sources

If a number doesn't match your chart, email me what you entered and what you expected, and I'll check it against the source. You can also read how the numbers are checked.

Checked by Paul Williams · Updated

Questions

What should the temperature split be?

It depends on how humid the return air is. Dry air gives a bigger split because more of the coil's capacity goes into cooling rather than drying it. At 75°F dry bulb and a 67°F wet bulb the target is 15.5°F; at 80°F and a 56°F wet bulb it's 25.0°F.

What does a split that's too high or too low mean?

Under Title 24's 2008 method, a split more than 3°F above target means airflow is probably too low: check the filter, blower speed, registers and ducts. More than 3°F below target means re-measure; if it's still low, airflow passes but the unit's capacity is probably low.

Is this still part of Title 24?

Not for compliance. Since 2013, Title 24 verifies airflow by measuring it directly, at least 350 CFM per ton for new systems and 300 for altered ones. The table stayed in the 2019 and 2022 editions for fault detection displays and was dropped in 2025. It's still a quick field check of airflow.

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