How To Tell if a Sealed Window Has Failed

Modern multi-pane windows are an integral part of a modern, energy efficient home's heating and cooling system. Utilizing two (or more) panes separated by either a vacuum or inert gas, the windows create an airspace that reduces the conduction of heat and cold through the window.

Modern sealed windows have a low failure rate and long life expectancy, but like any building product, they can occasionally suffer from problems. These can include loss of vacuum, condensation and even debris between the panes.

  • One simple way to determine if your sealed windows have failed is to perform a thorough visual inspection. Clean the glass panes both inside and out, and look closely at the panes themselves and the interior space between them. Cracks or chips along the edge of the panes, either the interior or exterior, indicate that the sealed window is likely to have lost its vacuum. Any condensation or traces of previous condensation (like white lines or rings, shadowy lines or hazing) between the panes also means the seal has probably failed.
  • In cases of severe failure, there can be debris or even cobwebs between the panes; these are certain signs that the window is no longer sealed, and will need repair or replacement.
  • If the visual inspection reveals no flaws, a further test is to use your hand to simply touch the interior panes of each window. A pane that is either much cooler during cold weather or hotter during hot weather than surrounding panes may have lost its seal. It can help to use a cooking thermometer, held in contact with the glass, to get more accurate readings, should one be available.
  • If a large number of windows have to be checked, or greater accuracy is required, it can be productive to obtain an inexpensive infrared non-contact thermometer for use in the testing. Using one of these thermometers is quite simple; just aim the sensor at the surface and press the measurement button, with the readout reporting in under a second or two on the exact temperature. This will allow for rapid, and fairly precise, measurement of a large number of windows with relative ease.

Sealed windows that have failed can, depending on the nature of the failure and the overall age and condition of the window, be repaired. This generally requires that the window unit, minus the casing and frame, be returned to the factory, although some service centers are capable of such repairs. Also, many good quality sealed windows come with specific warranty coverage regarding the seal. Be sure to check whether any windows that you find have failed are still covered by this type of warranty, and if they are, contact the manufacturer in regards to obtaining warranty repairs.


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