Air contains water in the form of vapors. When air temperature reaches a certain point (known as the dew point), air molecules become saturated with moisture, and vapors turn into liquid. That’s condensation, which explains how waterdrops form on windows as the warm air touches the much cooler glass surfaces and its dew point drops.
During the warmer months, condensation may occur on exterior window surfaces. Modern aluminum windows have exceptionally high thermal efficiency levels (low U-value). As they minimize heat flow to the outside, exterior surfaces remain cooler than the surrounding air. As a result, moisture forms on the glass, proving the window is energy efficient.
During the colder months, condensation may occur on interior window surfaces due to much lower outside temperatures. Aluminum windows and doors usually have the lowest temperature of any other surface in the house, causing the warm air to release humidity upon contact. That’s more likely to happen when the temperature gap between indoors and outdoors increases.
A newly built property can take up to 12 months to dry out fully. During that period, humidity levels are high as the various building materials release vapors. That moisture may condense on the construction’s cooler surfaces, like aluminum frames and glass panes.
Frost is caused by deposition rather than condensation. It occurs when air temperature is so low that water vapors turn directly into ice. Interior frost may form on non-insulated metal window frames but rarely occurs when insulation is in place. (Condensation, on the other hand, may appear both in insulated and non-insulated window frames.)
Metal windows and doors are never fully shielded against condensation and frost, but their causing factors can be minimized through construction and daily practices:
- Increase air temperature
- Heat interiors
- Insulate below and above bay, bow, and garden windows
- Send warm air towards windows through air ducts or increase air circulation with a fan
- Use radiant heating on walls and floors
- Increase ventilation
- Keep windows open and fans on during and after steam-producing activities
- Install/upgrade ventilation
- Keep blinds and drapes open
- Use ceiling fans
- Reduce humidity
- Use humidifiers cautiously or not at all
- Use a dehumidifier if necessary
- Avoid or limit plants, aquariums, and pets
- Ensure gas appliances don’t leak or malfunction
- Store firewood outside
- Avoid air-drying clothes inside
- Repair existing grading or drainage problems
