# Mixed Air Temperature Calculator

URL: https://speedycalculator.com/calculators/physics/mixed-air-temperature/
Last updated: 2026-10-30

> The mixed air temperature calculator finds the temperature of a blend of outdoor and return air from either the airflows or the percentage of outdoor air.

## Inputs

- Method
- Outdoor airflow (CFM, m³/h, L/s)
- Return airflow (CFM, m³/h, L/s)
- Outdoor air (%)
- Outdoor air temperature (°C, °F, K)
- Return air temperature (°C, °F, K)

## Results

- Outdoor fraction
- Mixed air temperature

## Formula

```
T_mix = (V_oa·T_oa + V_ra·T_ra)/(V_oa + V_ra) = x·T_oa + (1 − x)·T_ra
```

## Explanation

Mixing fresh outdoor air with return air is a quick way to estimate the air entering a heating or cooling coil. Building controls use the mixed-air temperature to manage economisers.

### How to use the Mixed Air Temperature Calculator

- **Method**
- **Outdoor airflow**
- **Return airflow**
- **Outdoor air (%)**
- **Outdoor air temperature**
- **Return air temperature**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose whether you know the airflows or the outdoor air percentage.

### Tips

- Use absolute temperature (K) in gas laws and efficiency formulas.
- Temperature differences are the same in K and °C.
- Heat = mass × specific heat × temperature change when no phase change occurs.
- Phase changes need latent heat at a constant temperature.

### Common mistakes to avoid

- Using °C in pV = nRT.
- Forgetting latent heat during melting or boiling.
- Confusing heat capacity (J/K) with specific heat (J/(kg·K)).

### Inputs explained

FieldWhat to enterMethodChoose one: Airflows, Outdoor air percentageOutdoor airflowUnits: CFM, m³/h, L/sReturn airflowUnits: CFM, m³/h, L/sOutdoor air (%)A numberOutdoor air temperatureUnits: °C, °F, KReturn air temperatureUnits: °C, °F, K

### Example values

How the main result changes when **Outdoor airflow** changes and everything else stays at the example values above:

Outdoor airflow (CFM)Mixed air temperature (°C)20025.222230025.736840026.250026.6196002780027.6667

## Worked example

Inputs — Method: Airflows; Outdoor airflow: 400 CFM; Return airflow: 1,600 CFM; Outdoor air temperature: 35 °C; Return air temperature: 24 °C.

Results — Outdoor fraction = 20 %; **Mixed air temperature = 26.2 °C**.

## Key terms

- **Outdoor air fraction**: Share of fresh air in the supply.

## FAQ

**Why is outdoor air added?**
For ventilation and indoor air quality.

**What is an economiser?**
A control that uses more outdoor air when it is cool enough to save energy.

**Is this the same as the psychrometric mixed air?**
It ignores humidity and density – fine for quick estimates.

**What outdoor air percentage is typical?**
10–30% for offices.

**What formula does the Mixed Air Temperature Calculator use?**
T_mix = (V_oa·T_oa + V_ra·T_ra)/(V_oa + V_ra) = x·T_oa + (1 − x)·T_ra.


## Sources

- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)
- [OpenStax – University Physics Volume 2](https://openstax.org/details/books/university-physics-volume-2)
- [HyperPhysics (Georgia State University)](http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html)