Mixed Air Calculator

Enter outdoor-air airflow, dry-bulb temperature, and relative humidity. Then enter the return-air values and select elevation-derived pressure or manual atmospheric pressure.

Current Weather can optionally populate outdoor dry bulb and relative humidity. The loaded values remain editable, and airflow always stays manual. Select Calculate Mixed Air to review the resulting state.

Mixed air is the condition produced after two air streams combine. In a typical HVAC system, outdoor ventilation air mixes with return air from conditioned spaces before the combined stream is heated, cooled, or otherwise conditioned.

Outdoor air introduces ventilation air and its current heat and moisture conditions. Return air comes back from conditioned spaces.

The proportions of the streams strongly affect the mixed condition. The displayed percentages use entered volumetric airflow, while the psychrometric calculation accounts for each stream's specific volume.

AnyHVAC calculates each incoming psychrometric state with the locked engine, converts airflow to dry-air mass flow using specific volume, conserves moisture and enthalpy, and derives the final state at the common project pressure.

Relative humidity is not directly averaged. It is calculated from the conserved mixed humidity ratio, mixed enthalpy, and pressure.

Dry bulb is ordinary air temperature; wet bulb reflects evaporative cooling; dew point indicates actual moisture content; and relative humidity compares vapor content with saturation at the mixed temperature.

Humidity ratio reports water-vapor mass per dry-air mass. Enthalpy represents moist-air energy, specific volume links air volume to dry-air mass, and OA/RA percentages show the entered volumetric proportions.

At sea level, mix 500 CFM of 90°F / 50% RH outdoor air with 1,500 CFM of 75°F / 50% RH return air. The implemented solver calculates:

Total airflow:

2000 CFM

Outdoor / return air:

25.0% / 75.0%

Mixed dry bulb:

78.7°F

Mixed relative humidity:

51.0%

Mixed humidity ratio:

74.7 grains/lb

Mixed enthalpy:

30.6 Btu/lb

Mixed-air calculations support outdoor-air ventilation reviews, AHU mixing-section analysis, economizer analysis, troubleshooting, commissioning, and estimates of the entering condition at a coil.

This V1 tool describes the mixed state only; it does not calculate coil loads or leaving-air conditions.