Do Home Replacement Windows Cause Condensation?

“I don’t know,” Marguerite sighed. She looked at her new home replacement windows. “The windows are beautiful, and we’re certainly warmer than ever before. Our energy bills are much lower. But there’s this fog on the windows almost every morning, and I hate it! Isn’t there anything that can be done?”

Condensation — the thin, silvery-gray watery film that clings to Marguerite’s home replacement windows — is nothing more than water vapor that accumulates on glass when it hits a cool surface. This water vapor comes from two sources: moisture in the interior air and the outdoor, exterior air.

Windows are not to blame for the appearance of condensation — but that’s hard to believe when one never had condensation before installing home replacement windows and has it often after installing the home replacement windows. Why does this happen? Did anything change besides your new windows?

Often, the answer is no — and there’s the problem. Condensation is formed, in part, due to the humidity inside your home. When you had older, leaky, less efficient windows, the humidity posed no problem. All that excess moisture just leaked out the window — along with up to 40% of your home’s heating and cooling energy. The moisture was gone, so you had no condensation.

But then, in an effort to save energy, reduce heating costs, improve your home’s aesthetic and any of a number of other reasons, you install home replacement windows. All of your heat is now staying indoors — but so is that moisture. The energy efficient windows, with double or triple panes of glass, specially coated glass and insulated gasses between the panels, help keep the damper air inside. Condensation accumulates as a result.

Occasional condensation happens. Physics can’t be denied, no matter what kind of windows you have. Throughout the year, when the seasons change or at times that there has been rapid, dramatic shifts in temperature, you will see condensation. This is to be expected.

However, if you have condensation occurring on a regular on-going basis, it may lead to problems. Few surfaces stand up well to repeated, prolonged exposure to moisture, although vinyl replacement windows fare best.

To reduce condensation in your home, you’ll need to remove some of the humidity from your interior air. This can be accomplished by using a dehumidifier, or by making sure that your home is adequately vented. Often, kitchens and bathrooms need the most aggressive venting, although attics and crawl spaces also require adequate air flow.

This news came as a great relief to Marguerite. She made a point of regularly using both her bathroom exhaust fan and the fan installed in the hood over her kitchen range. Additionally, she discovered that her dryer was not venting properly — a huge contributor to the humidity level in her home. She purchased a dehumidifier at her local home store for less than $100 and presto — the condensation was gone.

“Thirty years I’ve lived in this house,” she marveled, “and I never knew how moist it was.” Looking at her home replacement windows, she smiled. “But I guess it was easy to see with my new windows!”