Broken Thermal Seals

What is a broken seal (broken thermal seal) on a window?

A “broken seal” on a window is the description given when there is evidence of moisture condensation inside a window pane between the glass panels. However, the term is not completely accurate as the moisture condensation can be formed by either an actual broken seal, the inability of the window desiccating materials (typically silica) of absorbing the moisture of the air inside, or both.

The failure or “break” on the seal itself can not be seen, it typically happens on the adhesive applied on both sides of an aluminum thin frame that separates the two glass panels that form the thermal window pane. The absorption failure of the silica desiccating material cannot be seen either and it is actually a cause that is rarely known or advertised.

Moisture condensation inside a skylight.

The most obvious aspect of a broken seal or failure of absorption of the silica and the one most people are familiar with, is the presence of moisture condensation inside the glass panes between the two glass panels. This condition some times is clearly visible, especially if the window with this condition is next to a window that doesn’t.  

Other times, the climate conditions on the exterior and the interior of a home, will actually prevent moisture condensation from forming. When the moisture intrusion begins and the cycle of moisture condensation has not been repeated enough times, it is almost impossible to detect the condition as it is not clearly visible. Same with the failure of the absorption materials, because the moisture will increase or decrease as the expansion and contraction of the air inside the window continues. This cycle is known as “solar pumping” and it happens with the length of sunlight exposure during the day and lack of it during the night.

Solar Pumping causes the air inside the window pane to heat and expand (pressurize) during the day which releases small amounts of air by the pressure. The cool of the night causes the cavity to shrink or (depressurize) and it acts as a vacuum, drawing small amounts of air into the window thermal space. The air drawn in, will contain natural moisture which the silica will absorb until it reaches its expected life span and stop, causing the moisture to accumulate inside the panes. A company called Window Medics is one of the first companies to provide information regarding the failure of the silica desiccating materials on the internet to the general public. They offer a service to correct moisture condensation inside windows. Although personally I cannot confirm their claims about correction of the issue, their website offers information that merits some reading at www.defogit.com. Please use caution when selecting any service company to perform any type of work. Always ask for references and samples of their work.

When no moisture is present, the only way to find a broken seal or failure of absorption inside the glass panes is by carefully inspecting the glass for the stains that are left after moisture has dried. If enough cycles have been repeated where the moisture is there and then it dries, whitish stains, will sometimes be visible as streaks that run semi horizontal or vertical (depending on the amount of moisture) and others, as whitish speckles inside the panes. These stains will typically have a different depth perception between any dirt or stains on the exterior of the window and the stains between the panes.

So what is inside the panes and why do they have to be sealed?

On less expensive windows, typically the ones found on the shelves at Lowe’s and Home Depot, the sealed pane is just filled with air. The air cavity creates an insulating barrier to separate the climate changes of the exterior and interior of a structure. For an upgrade on the thermal insulation efficiency of a window, the manufacturer can also fill the space between the glass with gas. This is typically an upgrade and costs about $20 to $30 more per window for typical applications. However, windows filled with gas may and will also fail with time.

Should I replace the window or just the pane that has the moisture or stains?

A typical sliding vinyl window (4’x6’) will cost about $250 to $300 new off of the shelf. A replacement pane for a metal sliding window where only one pane is replaced, will cost approximately the same as a new vinyl window. Thus, buying a new window makes the most sense if you can afford the additional cost of installation (typically around $200 to $300) on top of the cost of the window.

What can happen if I decide not to change the window?

Thermal panes on windows offer better energy efficiency of a home and can decrease costs on heat and cooling consumption. However, historically, tangible energy efficiency changes can only be seen after regular usage of the home over a long time for comparisons to be applied. In my personal opinion, repairing a thermal pane on a metal frame window (Aluminum), is not worth the money as the metal itself is one of the best conductors of energy.

Aluminum is one of the worst insulating materials to have on a window and will transfer a lot of the exterior temperature conditions inside a home. Faced with the same choice, I would buy the vinyl window and either install it myself or pay the money to have it professionally installed. A vinyl or wood framed window will offer the best energy efficiency when compared to aluminum framed windows. Otherwise, living with a window that “fogs” or has moisture or stains, is just a matter or getting used to an eternally dirty window.

I encourage you to read carefully the window manufacturer’s installation instructions to familiarize yourself with the propper method of water proofing the window opening, and to double check that a contractor does the job right if you decide to pay for some one to do the work for you, if you decide to change a window with “broken seals.”  

What can I do to prevent “broken seals”?

Open and close the windows gently and at the minimum once a week for those windows that you would typically not open. Normal use will prevent some of the dirt build up and will ease the window movement, preventing added pressure on the frame when opening them

Use siliconized lubricant for moving parts and clean the hardware at least on an annual basis.

Avoid washing the windows with a pressure washer and clean the gliding surfaces at least once a month.

For additional information on the standards on energy efficiency of windows, doors, and skylights, visit the U.S. Department of Energy “EnergyStar” website at www.energystar.gov and their Energy Efficiency and Renewable Energy site at www.eere.energy.gov