Trained Eye


Fogged Window Seals


Dear Mr Marantz,

We read your articles fairly regularly and enjoy them very much for their concise and competent style and contents. That's why we believe you might be the man to ask for advice on our problem.

We have a 14-year-old house on the Red River in Winnipeg with huge, triple pane, heat mirror windows. One of the largest of these started showing condensation by the end of the winter. We are trying to find out whether this kind of window can be restored, i.e. pumped out and resealed. We believe the make of the windows is Willmar . There is a slight chance the bills are still around but we are not the original owner who built the house and we also have lost contact with him. But we do have a bundle of those bills.

We would be very grateful, if you could send us a brief answer - or, if you find it worth the while - make this topic a subject of a future article.


The question you have asked is indeed an excellent topic for an article and I hope the reply will be informative, but may not offer you much of a solution. Windows that have lost their seal cannot be resealed, as far as I know. I have never seen or heard of fogged window being refurbished.

Modern windows are quite energy efficient, compared to older, leaky sliders installed in homes over 30 years old. This is primarily due to good quality weatherstrips and hardware and sealed units for glazing. A sealed unit is a single glazing unit comprised of two or more panes of glass, with space in between, that is factory sealed with a vacuum or gasses installed between the panes. This sealed air space provides for a relatively effective thermal barrier to prevent heat loss through the window, during cold weather. The standard sealed unit is made up of two regular panes of glass, with an average 8mm to 12mm space in between. Higher quality units may have inert gas installed between the panes, three panes of glass, and/or coatings on the glass for better thermal resistance.

The “Heat Mirror” windows you have in your home are a trademarked name for a process of a specialized type of sealed unit. These high quality triple units had a special composite material installed for the middle pane, instead of glass. This material has reflective properties that transfers heat away from the warmer side of the widow. In the winter this reflects heat back to the interior of the warm house and to the exterior in the summer. This allows these windows to have better insulating properties and a higher equivalent R-value than all glass triple-pane units.

The fogging seen between the panes simply means that the factory seal has been compromised and air has leaked into the sealed unit. The fogging is from moisture contained within the air. The leak may be caused by a very small hole in the seal or a crack or damage to the glass or seal. If the window is not cracked or damaged, the thermal properties of the window may have changed little from the original installation. If inert gas such as Argon was originally installed, it may have leaked out and the window will have somewhat lower heat retention properties. It is not essential to have the windows repaired, but the view out the fogged panes will be a nuisance.

As stated above, there is no way that I am aware of to restore the seal and remove the moisture from between the panes of the sealed units. It is quite common for this to happen and most warranties on sealed units are around 10 years. Many sealed units will have stickers installed on the spacers between the panes or faint imprints near the corner of the glass, with date of manufacture. These may be hard to find, but once located, will give an actual age of the sealed unit and tell you whether they were original or replaced. A call to the manufacturer with this date and style of window will let you know if there is still a warranty applicable.

Unfortunately, the only way to repair a fogged sealed unit is replacement. These units are normally easily removed and replaced by removal of window stops, either on the inside or outside of the window. New sealed units can be ordered and made by most local window manufacturers, to fit any window. Removal and replacement by trained technicians can be done on site and usually takes less than an hour per window. The good news is that the entire window does not have to be replaced, as long as the frame and sash are still in good condition, just the sealed unit. This makes replacement much easier and less costly.




P.O. Box 69021
#110-2025 Corydon Ave
Winnipeg, MB
R3P 2G9