Mixed Air Temperature Calculator

Mixing two air streams gives a flow-weighted average temperature — common in ventilation.

How the Math Works

The Mixed Air Temperature Calculator uses a weighted average formula to determine the final temperature when two air streams combine. The calculation T = (Q₁T₁ + Q₂T₂) ÷ (Q₁ + Q₂) multiplies each air stream's temperature (T) by its respective airflow rate (Q), sums these products, and divides by the total combined airflow. This weighting ensures that higher-volume air streams have proportionally greater influence on the final mixed temperature, which accurately reflects how air mixing works in real-world systems.

Practical Applications

To apply this calculation, first measure the temperature and airflow rate (in CFM or similar units) for each air stream using a thermometer and an airflow meter. For example, if you have warm air at 70°F flowing at 400 CFM mixing with cool air at 50°F flowing at 600 CFM, plug these values into the formula: (400×70 + 600×50) ÷ (400 + 600) = 56°F. This calculation is essential for HVAC professionals designing ventilation systems, ensuring proper temperature control in commercial buildings, and verifying that air handlers deliver the expected mixed-air conditions.

Day-to-Day Use

Understanding mixed air temperature helps in everyday situations where air combines from different sources. You can use this principle to optimize your home's heating and cooling efficiency by determining the right mixture of fresh outdoor air and conditioned indoor air. It's useful when using fans to cool a room with open windows, where you might mix cooler night air with warmer daytime air. Even practical for cooking applications, like determining the temperature of air from multiple oven burners or understanding how mixing hot and cold air in a hair dryer affects styling results.

Worked example

300 CFM at 75 °F + 100 CFM at 40 °F → 66.25 °F.

FAQ