High humidity adds to the effects of a hot summer day

August 6, 2020

Humidity is the amount of water vapor in your home. Too much of it promotes mold, mildew and other biological growth that can lead to serious building damage and promote allergic reactions, asthma attacks and even pneumonia.

Relative humidity is the amount of water vapor in the air compared to the amount the air can hold at a given temperature. Generally, we’re most comfortable in a 30 to 50 percent range. Two factors affect relative humidity: the amount of moisture in the air and the temperature of the air. Relative humidity increases when the amount of water vapor in the air increases or when the air temperature drops. The capacity of air to hold water changes with temperature. The warmer the air, the more water vapor it can hold. The colder the air, the less moisture it can hold.

As the Missouri Department of Natural Resources explains, you feel cooler in a room at 75 degrees with 25 percent relative humidity than in a room at 75 degrees with 40 percent relative humidity. Consequently, in summer less humidity in the air makes you feel cooler, hence the use of dehumidifiers that remove excess moisture. In winter, more humidity in the air makes you feel warmer and less likely to raise the thermostat setting, hence the use of humidifiers that add moisture.

You can measure the relative humidity with a humidity meter, affordable and available at hardware and big box stores and many online sources.

According to the Environmental Protection Agency, a sure sign of too much moisture is condensation on the inside of windows. Condensation occurs when the relative humidity of the air reaches 100 percent, and the water vapor in the air changes to water.

Most interior moisture comes from bathing, cleaning, cooking and water evaporation and emission. Outside moisture enters through leaks in your home’s shell.

Now that it’s summer, here are some tips from DNR and the University of Florida Extension for removing moisture from your home:

Look for the source by checking for stopped-up drains, leaky plumbing, washing machine hoses, shower tile grout, water heaters. Look for outdoor air coming in through windows, doors, electric outlets, air conditioning units. For the latter, make sure the filter is not clogged and the evaporator cooling coils are not iced over. To correct problems:

  • Weatherstrip and caulk to fix leaks in and around the roof, walls, windows, doors, outlets, air conditioning units and pipes
  • Add ventilation fans in the kitchen, bathrooms and laundry rooms, and vent your clothes dryer to the outside
  • Use exhaust fans about 10 minutes to remove moisture and odors after bathing or showering
  • During humid weather, run your air conditioning regularly but if the nighttime low is forecasted to be 55 degrees or below, open windows
  • Properly vent attic and crawlspaces, and cover exposed earth in crawlspaces with a vapor barrier
  • Install downspouts that flow away from the foundation
  • Slope the grade away from the house
  • If you have single-pane windows, install storm panels, double-pane insulating glass or triple-glazed panels
  • Repair stopped-up drains and leaky plumbing, hoses, shower tile grout and water heaters
  • Look for outdoor air coming in through windows, doors, outlets and air conditioning units
  • Reduce the number of house plants and pilot lights

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