Homeowners who have highly energy-efficient windows may notice condensation forming on the outside under certain weather conditions.
Why is my bedroom window covered in condensation from the outside early in the morning?
This question is often asked by homeowners who have highly energy-efficient windows. This condition usually occurs in late summer and early fall when the night time temperature drops several degrees.
The moisture on the outside of the window is condensation. It will soon evaporate when outside temperature rises. As we know, condensation happens on cold surfaces. During the night, if the outside temperature drops below the dew point then condensation forms. The fact that the condensation is forming on the windows means that very little heat from inside the house is escaping through the windows. That's a good thing and proof that you have energy-efficient windows.
When the temperature of the exterior surface of the glass is cooled below the dew point of the outside air, moisture forms on the exterior side of the glass. Then, as the glass temperature rises above the dew point, the moisture evaporates back into the air.
Three main conditions promote exterior condensation:
- High outdoor humidity
- Very limited or no wind
- Clear night sky
How to Control Exterior Condensation?
- Close window coverings to reduce cooling of the glass by air-conditioning.
- Remove or trim outside shrubbery near glass to promote air circulation.