Methods of Humidity Generation

There are three common ways of creating moisture for humidity control in test chambers. Let’s review they types and the benefits and limitations of each.

Steam GeneratorType 1: “Steam Generator”

A steam generator is a tank with an immersion heater. As the water in the tank is heated, steam rises up a tube to the chamber’s mixing plenum (where the main heaters and cooling coil are). The chamber, based on humidity demand, controls the output of the heater.


  • High volume of moisture can be generated (good for large chambers)
  • Quality of water vapor is consistent


  • Large amount of water to heat delays initial steam supply
  • Needs to be nearly boiling to generate steam for even moderate humidity levels
  • Constant boiling leaves excessive deposits of minerals
  • Must disassemble for inspection/cleaning
  • Larger heater required for generating steam

AtomizerType 2: “Atomizer”

Atomizers use a fine-spray nozzle to “atomize” the water. This is done in the mixing plenum. As the atomized water passes the chamber heater, it becomes heated to a gas.


  • Very simple system
  • Can provide high volume of moisture
  • No problems with heater burn-out
  • Said to save electricity because water isn’t directly heated
  • Cools the air (beneficial when needed)


  • Potential for clogging of spray nozzle
  • Water droplets must be fully heated to vaporize
  • Dependant on water quality supplied
  • Difficult to produce high-humidity at higher temperatures
  • Minerals in the water result in fine dust throughout the chamber

Type 3: “Water bath”

Like a steam generator, but not in an enclosed box. A small “bath” is located in the mixing plenum. As the chamber air is drawn into the plenum, it passes the bath, picking up vapor.


  • Quick response due to small water amount
  • Doesn’t have to be at boiling to provide moisture
  • Less boiling means less mineral deposits to clean
  • Can be inspected and cleaned quickly


  • Can’t generate high-volumes of moisture
  • Constant presence of water in bath during humidity tests can make low-humidity control difficult.

Now, you are wondering, which does ESPEC use? All three, depending on the application. For our standard chambers, we use the water bath system. For larger systems, we use the steam generator. And for certain low-temperature, high-humidity applications, we use the atomizer.

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