Absolute and relative humidity

Insulation · The Basics · printed page 233 (PDF page 234)

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Book index entries

Absolute and Relative Humidity Relative Humidity Insulation – the Basics

Text in the illustration

1
air at 70°F (saturated)
grains of moisture
1 pound of air
1 lb
70°F
absolute humidity = 108 grains / pound
relative humidity = 108 grains / 108 grains (saturated) = 100%
2a
air at 40°F (saturated)
40°F
absolute humidity = 36 grains / pound
relative humidity = 36 grains / 36 grains (saturated) = 100%
warm it up
2b
air at 70°F
relative humidity = 36 grains / 108 grains (saturated) = 33.3%

Generated explanation

Three schematic air samples sit on scales marked 1 lb, with dots representing grains of moisture and dashed outlines representing the air volumes. The saturated 70°F sample contains 108 grains of moisture per pound and has 100% relative humidity. The saturated 40°F sample contains 36 grains per pound and also has 100% relative humidity. An arrow labeled “warm it up” connects the 40°F sample to a 70°F sample: moisture content remains 36 grains per pound, but relative humidity drops to 33.3%. The illustration compares moisture content and relative humidity at different temperatures rather than showing a building assembly or defect.

Components

schematic air samples weighing scales