Relative humidity (RH)
The ratio of the water-vapor pressure in air to the saturation vapor pressure at the same temperature, expressed as a percentage. Temperature matters: heating air without adding moisture lowers its relative humidity.
Cubic feet per minute (CFM)
A measure of airflow. In load calculations, outdoor-air exchange helps determine how much moisture must be added. A circulation fan’s CFM describes air movement within the space and is not automatically the same as outdoor-air exchange.
Air changes per hour (ACH)
The hourly air-exchange volume divided by the building or zone volume. Multiplying building volume by ACH gives cubic feet per hour. The FanMist guide uses an estimated ACH when measured exhaust or makeup-air data is unavailable.
Makeup air and infiltration
Makeup air is deliberately supplied to replace air removed by exhaust systems. Infiltration is uncontrolled outdoor air entering through openings or leaks. Both affect the winter moisture load; their relationship depends on the building’s air balance.
Humidification load
The rate of water-vapor addition needed to maintain the specified indoor conditions, commonly expressed in pounds per hour. It differs from the final equipment capacity, which can include a design margin.
Grains of moisture
A grain is a unit of mass: 7,000 grains equal one pound. Always read the denominator. Grains per cubic foot and grains per pound of dry air describe different quantities.
Equilibrium moisture content (EMC)
The moisture content at which a material neither gains nor loses moisture under the surrounding conditions. Wood and paper move toward equilibrium with their environment; the rate and resulting behavior depend on the material and conditions.
Atomization and evaporation
Atomization breaks liquid water into small droplets. Evaporation changes liquid water into water vapor. A visible mist is atomized liquid water; humidity describes water vapor in the air.
Loading ratio
In the FanMist nozzle guide, the fan’s airflow in CFM divided by the mist-ring output in lb/hr. It helps relate water output to the available moving air.
Adiabatic humidification
Evaporative humidification in which water draws heat from the surrounding air as it becomes vapor. High-pressure water misting is one approach; steam systems use an external heat source to vaporize the water.
Source documents
Read the original tables, procedures and specifications in the supplied IHC references.
FanMist master glossary · complete reference · PDF ↗Woodworking load calculator guide · PDF ↗High-pressure nozzles · PDF ↗Put the guidance to work.
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