December 24, 2025, 12:06 pm | Read time: 4 minutes

Typical Signs of Outdated Windows

Especially in the cold season, it becomes apparent whether windows still insulate effectively. Those who regularly notice condensation on the panes or suffer from noticeable drafts should take a closer look at their windows. According to the Association of Windows + Facades (VFF), such signs often indicate poor thermal insulation.

A look at the product marking embossed in the edge seal of the window pane can already provide initial clues. The manufacturing year of the glazing is usually noted there as well. Glass produced before 1995 is generally considered energetically inefficient.

How the Lighter Test Works

If no production year is visible, a simple test with a lighter or a candle can provide information about the type of glazing. It involves the number and color of the flame’s reflections:

• Single glazing (up to the 1970s): Two closely spaced reflections of the flame, no discoloration, indicate single-glazed windows that provide little insulation. Replacement is strongly recommended, as the savings on heating costs quickly pay off.
• Double glazing without thermal protection coating (before 1995): Four reflections in two pairs of the same color are visible. Here, too, the insulating effect is low, and a replacement can significantly improve living comfort.
• Double glazing with thermal protection coating (from 1995): Also four reflections, but the second flame appears slightly violet. The coating provides better thermal insulation—replacement is usually not necessary.
• Triple glazing with thermal protection coating (from 2004): Six reflections, grouped in three pairs. The second and fifth flames appear slightly violet—an indication of modern thermal protection glazing.

Drafts as Another Warning Signal

Another indication of leaky windows: If the flame flickers strongly during the test, it may indicate leaky spots. The cause is often damaged seals or poorly adjusted fittings. The window seals may no longer be functioning properly and need to be replaced. The fittings may also not be in good condition. In this case, a professional service should be consulted for maintenance.

More on the topic

Old vs. New What to Consider When Replacing Windows

Spring Checkup Why Now Is the Perfect Time to Maintain Your Windows

When New Windows Are Worth It

Whether the replacement of old windows is worthwhile depends, according to the association, on the condition of the building, the size of the windows, and current energy costs. VFF Managing Director Frank Lange gives a clear recommendation in a press release: “Anyone who still has windows with single glazing or even insulating glazing without thermal protection coating older than 1995 should definitely consider modernizing with new windows.” In many cases, the investment pays off through lower heating costs after just a few years.

Additionally, further measures such as sound, sun, or burglary protection can be integrated during modernization. In Germany, the state BEG individual measures funding continues to support window renovations with up to 20 percent of the investment costs—a financial incentive that can make the decision for new windows easier.

Glazing Instead of Replacing the Entire Window

A complete window renovation is not always necessary: If the frame is still intact and the window closes reliably, it can, according to the Consumer Center, also be sensible to only replace the glazing—provided it does not yet have a thermal protection coating.

This measure is not only more cost-effective than a complete replacement but also preserves the building’s exterior appearance. However, the condition is that both the fittings are fully functional and the existing frame is stable enough to accommodate the heavier modern window panes.

With material from dpa