Managing moisture in your home



bret curry

Bret Curry is the residential energy
manager for Arkansas Electric Cooperative

 Happy New Year! I wish you all the best for an abundant, healthy and energy-efficient year.

We had a taste of winter in mid-December, which prompted recurring questions like, “Why do windows sweat?” Or, “Why is the bottom part of the window frame covered with moisture?” The simple answer is it’s due to moisture inside the home.

Our laws of nature are at work year-round, and moisture vapor inside our homes that’s generally invisible in the summer can become quite visible in the winter. Furthermore, during the winter, as the outside temperature drops below the set-point on the home’s thermostat, the warm air from our heating system moves to cold. Also, a warm interior will allow air to expand and retain more moisture. Remember, heat moves to cool and moisture moves to dry.

Infrared reveals heat loss (purple) where the window frame meets the glass.

Condensation develops on this cold window frame.

In many homes, the weakest link in the thermal barrier is the windows. Heat can escape from the jambs, frames and glass, causing those areas to become cold (image 1). Whenever warm, moist interior air comes in contact with the cold surface, the air temperature drops below the dew-point, and then moisture changes state. What was once an invisible vapor now condenses and becomes a noticeable liquid (image 2). Many of you may even recall older, aluminum-framed windows that developed frost on the inside. This happens when water vapor within the home changes state to a liquid, then changes again into a frozen mass.

When troubleshooting this slippery moisture problem, we need to identify all the sources of water within the home. Everyday behaviors like showering, bathing, cooking, baking and even breathing will add moisture into the air. Even wet towels hanging from the towel bar will add moisture to a home. Furthermore, toilet bowls, aquariums, pet watering bowls, steam irons, coffee pots and many more items also contribute moisture. Leaky homes with unwanted air infiltration and homes that have vented crawlspaces without moisture barriers can cause moisture from outdoors to migrate into a home when the outside humidity is higher outside than within. Left unaddressed, the long-term effects of a moisture nuisance can lead to rotten sill plates and construction damage around the window.

Here are some simple, do-it-yourself solutions that can help with winter moisture problems.

  • Always run the ventilation fan in the bathroom during and after showering and bathing. If you don’t have bathroom fans, be sure to install them and run the ducting to the outside.
  • Check to make sure the dryer vent is connected to the unit. As crazy as this may sound, a disconnected dryer vent is not uncommon. Make sure the vent pipe does not have any holes and is vented to outside.
  • Repair weather-stripping around all doors. Caulk and seal leaky window frames. Repair and replace broken window panes.
  • Always use a vent-a-hood or downdraft ventilator when cooking, especially on spaghetti night or when boiling water. In order to evacuate unwanted moisture, these ventilation systems must be vented to outside.

Unvented natural gas or propane log systems contribute moisture as a byproduct of operation. Consider vented systems. Also, for heath and safety, always install a carbon monoxide detector in proximity of these devices.

  • Acquire an inexpensive, indoor thermometer with a hygrometer, which measures humidity, to monitor actual conditions within your home. These are available at box stores and online.

New windows could be in your future. However, I recommend a comprehensive energy audit before making this expensive investment. Be sure to read our Building Guidelines for Energy Efficiency booklet (available for download at