Free Online Humidification Load Calculator

Winter and process spaces often need moisture added to reach a target relative humidity. This calculator sizes the humidifier from the airflow and the rise in humidity ratio between the incoming and target air, giving the moisture load in kg/h, following ASHRAE Fundamentals.

The load is simply the mass of dry air handled multiplied by the increase in its moisture content. Cold outdoor air holds very little moisture, so the required humidity-ratio rise - and the humidifier capacity - is largest in winter and for high-ventilation spaces. Steam humidifiers add moisture without cooling the air; adiabatic (water) humidifiers also cool it, which can be useful or must be reheated.

Example: An AHU handling 2 m³/s of air (about 8640 kg/h dry air) must raise the humidity ratio from 0.003 to 0.007 kg/kg to reach the winter target. Moisture load = 8640 × (0.007 − 0.003) = 34.6 kg/h of steam or water, which sizes the humidifier and its water/steam supply.

Choose the humidifier type to suit the air condition and hygiene needs:

Design Notes

Winter humidification loads are the largest because cold outdoor air is very dry. Provide enough absorption distance downstream of a steam lance before the next component or sensor, treat water on adiabatic systems to prevent scaling and biological growth, and interlock with the AHU so the humidifier only runs with airflow.

Indicative guidance - confirm targets against the process or comfort humidity band.