What's Dew Point? - Water Damage Restoration


Here is a typical discussion you will hear in Dennis Klager’s IICRC WRT Class. Join us!


Whether evaporation or condensation happens depends on heat energy. Temperature is a measure of this “heat energy”.


Water drops are made of huge numbers of vapor molecules. The vapor molecules are held or bonded to the drop and need energy to escape this “hold” or “bond”. Given enough energy, a molecule will overcome the “hold” of the drop and escape to become a vapor molecule out in the space of the room. 


Vapor needs heat energy to remain as vapor. When the heat of the molecule (energy) decreases it can get to a low enough energy level where it goes back to the drop. It has reached the “Dew Point” (condensation). Here, or below, we have condensation, the formation of water. So……at the “Dew Point” there is not enough heat energy to support the vapor molecule… goes back to the “hold” of the drop.

Many temperatures can exist, on various surfaces, in a room, at many different times, depending on the temperature or “heat energy” at the various surfaces. This is because different materials have different heat conductivity rates and will have different temperatures than each other. They will reach “condensation” at different times.


NOTE: Temperature above dew point…… evaporation; temperature below ……condensation.


Just as, 7, in pH, is the spot where acid and alkaline stop and start, evaporation and condensation start and stop at the Dew Point. The comparison ends there.


If you could see blue arrows for condensation and red arrows for evaporation happening in a room, there would be hundreds going into different materials and coming out of different materials, at the same time. This is happening now where you are sitting - or standing, or laying down. :)


Obviously, on a water damage restoration job, we want the surface temperature of the wet materials above the condensation temperature…..substantially. Evaporation happens when vapor molecules escape that "hold".For every 20 degree increase above, the evaporation rate is doubled. That’s huge!


Condensation is a consideration on a cold day if you have the door open, for any reason. If condensation, or lower, is reached by the various materials in the front foyer, there will be condensation (water) on walls, furniture and hard surface floors. Moving moisture sensitive items, in the area, to a drier location, would be a good thing.


When evaporation happens, some heat is taken by the escaping vapor molecules. This is the theory of refrigeration. Inside the coils, evaporation happens and makes cold. This is what brings the coils to the condensation temperature, or below. When warmer, wet, vapor hits the cold coils the vapor temperature is brought to or below the dew point and condensation forms. This is how the dehumidifier removes vapor from the space, it is operating in.

By staying at or below dew point temperature we have constant condensation and……..dehumidification.


            Dennis Klager

            Water Damage Restoration Instructor


Copyright 2012 by Dennis Klager