Understanding Condensation on Windows

Ever wonder why condensation forms on your windows, and what you can do to prevent it?
Under certain conditions, condensation can form on the exterior or on the interior panes of dual insulating glass.
The Frequently Asked Questions and Answers below will give you a better understanding of condensation, and how it can be minimized.

Minor Condensation on Window Glass

Shown: a moderate amount of condensation on interior glass pane

About Interior Pane Condensation:

Q: What causes condensation to form on the interior glass of my windows?

A: Whenever there is excess humidity in a home, it manifests itself in the form of condensation on very cold surfaces which, in winter, will be your window glass.  The warmer the air in your home, the more moisture it will retain. When this moist air comes in contact with your relatively cold window glass, it is quickly cooled, resulting in droplets of water.

Q: Do windows themselves cause condensation?

A: No, condensation is not the fault of the window. All window surfaces except for the glass are at a relatively warm temperature. Even the best insulating glass is still the weakest link in the insulation chain of any window. In fact, replacement of old drafty windows and doors with new, better sealing units reduces air flow through the home, making it tighter, and so able to retain more moisture.

Q: Where on a window does condensation normally form, and why?

A: Condensation always begins to form at the bottom of the glass pane.  This happens because when the warm (and moist) air from the room contacts the cold glass surface, it begins to cool. Cool air tends to fall and by the time it hits the bottom of the glass it has cooled enough to condense. This has a cumulative effect.

Major Condensation On Window Glass

Shown: a severe amount of condensation on interior glass pane

What Can I Do About It?

#1: Control the humidity levels in the home and increase air movement!

  1. Use exhaust fans in the high humidity areas: kitchen, bathroom, laundry room
  2. Clothes dryers and gas burners must be vented to the outdoors
  3. Use furnace or room humidifiers sparingly, if at all.
  4. Ventilating louvers in attic, basement, and crawl spaces must be open and correctly sized
  5. Keep fireplace dampers open at all times during winter to allow moisture laden air to escape. (Warm air naturally rises)
  6. Air out your home a few minutes each day

#2: Upgrade the glass in your windows

If your windows are mechanically good but use regular insulating glass, upgrade to warmer, Low-e coated glass, with “Warm Edge Spacer” technology. Windows with standard glass used a thermally-conducting aluminum spacer (separating the two panes of glass), around the perimeter. This resulted in very cold glass temperatures at the glass edges, making the condensation problem worse.  Today, we use thermally insulated spacers resulting in a much warmer glass surface at the edge, resulting in reduced tendencies towards condensation.
We can supply this superior replacement insulating glass! Details HERE

No condensation on window glass

Reduce humidity in your home and upgrade your glass for a crystal clear view all year long!