Understanding Window Condensation
One of the most common concerns homeowners have after installing brand-new, highly efficient windows is seeing water droplets form on the glass. Many people assume their new windows are defective. In reality, in almost all cases, condensation is proof that your new windows are doing exactly what they are supposed to do: providing a tight seal.
However, where the condensation occurs tells you exactly what is happening. There are three types of window condensation:
1. Interior Condensation (Room-Side)
When water droplets form on the inside of the glass (inside your house), it means the warm, moist air inside your home is hitting a cold surface.
Why it happens:
Older, drafty windows allowed dry outside air to constantly leak into your home, reducing indoor humidity. They also let your warm air leak out. New, energy-efficient windows create a tight seal. This traps the moisture from cooking, showering, and breathing inside your home. When that trapped humidity hits the glass on a cold winter day, it condenses into water.
Is it a window defect?
No. It is a humidity issue inside your home.
How to fix it:
- Lower the setting on your whole-home humidifier in the winter.
- Run bathroom exhaust fans for 20 minutes after showering.
- Use your stove hood fan when boiling water.
- Open blinds and curtains during the day to allow warm air to circulate against the glass.
2. Exterior Condensation (Outside)
When you wake up on a cool fall or spring morning and see condensation on the outside of your windows, it can be startling.
Why it happens:
Exterior condensation occurs when the temperature of the outside glass drops below the outdoor dew point. Because your new windows are so incredibly efficient (low U-Factor), the heat from inside your house cannot escape through the glass to warm up the outer pane. The outer pane stays as cold as the outside air, causing the morning dew to collect on it—just like it does on the windshield of a car.
Is it a window defect?
Absolutely not. In fact, exterior condensation is a badge of honor. It proves that your Low-E coatings and argon gas are working perfectly to keep your expensive indoor heat trapped inside your home, rather than leaking out to warm the outside glass.
How to fix it:
You don't need to do anything. As the sun rises and warms the outside air, the condensation will naturally evaporate.
3. Between-the-Glass Condensation
This is the only type of condensation you need to worry about. If you see fog, haze, or water droplets between the panes of glass where you cannot wipe them away from the inside or the outside, you have a problem.
Why it happens:
This means the perimeter seal of the insulated glass unit (IGU) has failed. The argon or krypton gas has leaked out, and moisture-laden outside air has seeped in.
Is it a window defect?
Yes. This is a seal failure.
How to fix it:
The glass unit must be replaced. Fortunately, most reputable manufacturers offer a 10-year, 20-year, or lifetime warranty on seal failures. If you purchased a certified window (such as a Window Wise certified installation), you will have robust warranty coverage to get the glass replaced at no cost.