# Liberal Arts Blog — The Happy Medium of Relative Humidity

Liberal Arts Blog — Monday is the Joy of Math, Statistics, and Numbers Day

Today’s Topic — The Happy Medium of Relative Humidity

What is the ideal relative humidity in winter and summer? When do you feel happiest out on a walk? How about indoors? Experts — please chime in. Correct, elaborate, elucidate.

INDOORS: BROADLY 30–40% IN WINTER, 40–50% IN SUMMER, BUT DEPENDS ON OUTDOOR TEMPERATURE

1. Too high: mold, damage to floors, furniture, musical instruments. Condensation forms on windows and what you don’t see is the damage within walls to sheathing and studs.

2. Too low: dry skin, itchy eyes, damage to floors, furniture, musical instruments. The drying of nasal passages leads to susceptibility to colds and to nose bleeds.

3. Winter: if the outdoor temperature is 20–40 degrees, the ideal is no more than 40%, if the outdoor temperature is 0 to 10 degrees, ideal is no more than 30%. If 10 to 20 below zero, then no more than 20%.

TECHNICALITIES — WHAT DOES RELATIVE HUMIDITY MEAN?

1. At 100% relative humidity the air is completely saturated. It is at its dew point. Absolute humidity is the absolute amount of water in a parcel of air — measured as grams per cubic meter

2. So dew forms in the morning when the air is coolest. The cooler the air the less water it can hold.

3. Relative humidity is determined by pressure as well as temperature.

NB: ideal thermal comfort is also a function of clothing, metabolic rate, and airspeed. The image above is that of a sling psychrometer used to measure indoor humidity. Below is an image of a hair tension hygrometer. Apparently, accurate measurement of humidity has been a tricky business. (See last link)

OUT FOR A WALK IN CONCORD, MA IN JULY

1. 95 degrees and 40% humidity — ok.

2. 85 degrees and 85% humidity — brutal.

3. 95 degrees and 85% humidity — stay inside.

Relative humidity

Fixit: What is the ideal winter indoor humidity level?

Ideal Humidity in Winter vs. Summer

Hygrometer

So what are your personal favorite magic numbers? What do they stand for? Please share the coolest thing you learned this week related to math, statistics, or numbers in general. Or, even better, the coolest or most important thing you learned in your life related to math.

This is your chance to make someone else’s day. And to consolidate in your memory something you might otherwise forget. Or to think more deeply than otherwise about something dear to your heart. Continuity is key to depth of thought.