It’s that time of the morning when you see it – the hazy, milky layer that cannot be removed from the window panes with any cleaning. You take the glass and wipe it inside and then outside, and the smog just refuses to go away. It’s not on the surface, that’s why. It sits within this, between the two panes of your double pane window.
It’s one of the most frequent window issues that dwellers in Toronto can experience, particularly in homes built 10 to 20 years ago. Though it may appear as a simple cosmetic problem at the moment, foggy windows between panes are an indicator of a more serious structural problem, one that will impact your home’s energy efficiency, comfort, and maintenance expenses.
Here’s what you can do to find out exactly what causes window fogging, how to determine if the fogging has already gone too far, and what your replacement options are.
What Is Actually Happening Inside a Double-Pane Window?
To understand why windows fog up between the panes, you need to understand how a double-pane window – technically called an insulated glass unit or IGU – is constructed.
A double pane window is a window with two panes of glass that are separated by a spacer bar, usually of aluminum or composite material. A space between the panes is filled with an inert gas (usually argon, sometimes krypton), and the whole assembly is sealed around its edges. Modern windows are made with this sealed space filled with a gas that provides thermal insulation. It reduces heat loss, decreases cold drafts at glass and helps prevent condensation on the inside of the glass.
Two layers of sealant hold things together around the perimeter of the unit. The primary seal (polyisobutylene) keeps moisture vapour from penetrating the cavity. The secondary seal, usually silicone or polysulfide, ensures structural integrity and bonding between spacer and glass. A desiccant material is placed inside the spacer bar which is a moisture absorbing compound that traps any moisture that may seep into the system in time.
With proper operation the inside of the IGU remains dry and free of dust for many years. When the seal fails however, the desiccant is overloaded and moisture starts to enter and condense within the unit and that’s when the fog will appear.
The Root Causes of Failed Window Seals
Sealing failure of windows does not occur in a single instant. It is caused by stress over the years on the sealed unit. Knowing the causes can help you determine if your windows are in jeopardy and options to replace them.
Thermal Pumping
It is the most common cause of IGU failure. As the temperature changes, the gas inside the window will expand and contract each day. This causes the pumping action (literally in and out) to put stress on the perimeter sealant over thousands of cycles. The weather in Toronto is harsh with the dramatic changes in temperature between seasons and also between day and night speeds up the process.
UV Exposure and Sealant Degradation
South and west facing windows are exposed to secondary silicone sealant that secures the glass to the window spacer. UV radiation can alter the molecular structure of the sealant over the years, leading to hardening, cracking and loss of adhesion. When the secondary seal is compromised, moisture vapour is able to enter the unit.
Improper Installation
Windows that were not installed with sufficient clearances for movement of the frames, or with the wrong shimming, flashing, can cause excessive mechanical stresses on the IGU. This is a physical stress that speeds up windows’ degradation and can lead to premature failure in 5 to 8 year old windows.
Cleaning Products and Chemical Exposure
Some homeowners are unaware that window sealants can be adversely affected over time by some types of cleaners, particularly those containing ammonia and petroleum-based solvents. This is particularly the case with spray and wipe cleanings performed over the years at the edge of a window or at the frame-to-glass seal where the overspray gets repeated contact over years.
Age
Although the installation is flawless and care is taken with the sealing device, IGU seals still have a limited life. Most manufacturers are able to give a 15 to 25 year warranty on their sealed units, assuming normal circumstances. The moment of failure for a seal is when it reaches the end of its service life, not if.
Recognizing the Stages of IGU Failure
All fogged windows don’t experience the same degree of failure. Knowing your place on the spectrum will help you determine if you need to act now or have some time to plan.
Early stage: Slight haze is visible between panes, particularly in the morning light or when there is a large difference in temperature between the inside and outside. The desiccant is saturated, yet still has some capacity. One window might be clear at certain times during the day.
Mid stage: Fog is present and persists during the day. As the water evaporates and condenses over and over again, it deposits the dissolved minerals from the air in a pattern of white or grey streaks on the inside glass surfaces, which can start to be visible.
Late stage: Interior glass surfaces are stained so heavily or are covered with white mineral deposits or permanently cloudy and the view is severely impaired. By now, the insulating gas has been completely lost, and the window is near single pane efficiency. The desiccant has been used entirely.
Failure of an IGU at this late stage means you are losing a significant amount of heating energy through this window. That loss can be quantified on your winter bill in Toronto.
Can Fogged Windows Be Repaired? The Honest Answer
Once homeowners see condensation between window panes, their initial thought is that it needs to be repaired and not replaced. There are companies that provide defogging services which include drilling tiny holes in the IGU, introducing a cleaning solution to clean the mineral deposits and then sealing the holes with one-way valves.
The truth: Defog is a symptom treatment, not a cause treatment. Not a successful seal, which implies that the insulating substance is depleted and the unit has actually lost its thermal performance. Even defogging can give a better optical clarity for a short time, but cannot restore the R-value of the window, will not return argon gas, or correct the failed seal. The fogging will likely continue after 1-3 years.
For the majority of homeowners with failed window seal repair, it is more practical and economical to replace the IGU or window completely, depending on whether the window frame is structurally sound or if the frame has signs of wear, air infiltration, or damage.
IGU-Only Replacement vs. Full Window Replacement
When it comes to replacing fogged double-pane windows, a decision that homeowners must make is whether to replace just the glass or the entire window.
Only replacing the IGU is appropriate if the structural condition of the window frame is good, it is not older than 15 years, properly airsealed, and the failure is limited to the IGU. A glazier or window company can order a custom sized replacement IGU and then fit it into the existing frame. Generally more economical than replacement windows and least disruptive to the interior trim and finishes.
Full window replacement is also the recommended solution when the window is over 20 years old and likely to need additional replacements in the near future, when the window needs the glass specification to be upgraded (adding triple pane, better low-E coatings or gas fills), or when multiple windows are being replaced as part of a larger renovation project.
When considering window glass replacement in Toronto, a professional evaluation is a necessity before making either of the above decisions. A trained installer can inspect the frame condition, make an accurate measurement of your existing unit and recommend a cost-effective, long-term solution for your individual situation.
When Replacement Is the Right Call
Many times the best – and not only the most convenient – solution is to replace a cloudy window pane with a new window unit.
If windows were installed in the home during the 1990s or early 2000s, the odds of the others being on the verge of failure are high. Replacing a window one at a time, one after the other, as they break is often more disruptive and more expensive than a planned replacement program. Modern windows also feature much better glass packages with triple-pane windows, enhanced low-E coatings, and improved spacer systems that drastically cut thermal bridging, making the energy savings from upgrading much more worthwhile.
If you notice fogging along with any other of the following symptoms, the window assembly is at the end of its life: drafts, condensation forming on the inside surface of the glass (not between the layers of glass), visible deterioration of the frame, or window that is hard to open and close.
IGU replacement Toronto experts can inspect your entire window collection on one visit and provide a clear understanding of what windows require immediate repairs, are near the end of their life, and have a long lifespan ahead of them.
Frequently Asked Questions: Foggy Windows Panes
Q: Is foggy glass between the panes a health or safety concern?
Fogging is not a health risk in itself. It is possible however, that over time, moisture may build up within a failed unit allowing humidity levels to rise at the window area that can lead to mould growth on adjacent surfaces like window sills and interior trim. Promptly handling failed units minimises this risk.
Q: How long does it take for a window to go from first fogging to complete failure?
Exposure to climate conditions, the orientation of the window and the initial quality of the IGU are all variables that influence the length of the timeline. Early stage fogging can last for 1-3 years. When mineral staining or excessive cloudiness is detected, the unit is in the last stages of failure and should be replaced.
Q: Will replacing fogged windows lower my energy bills?
Yes, especially in a climate such as that in Toronto. A late-stage failed IGU has a similar thermal efficiency to a single pane window. A modern double or triple pane, low-E glass argon filled window can make a significant difference in heat loss through the window and provide better comfort around the windows in the winter months.
Q: Do I need to replace the entire window if only the glass is fogged?
Not necessarily. An IGU-only replacement will fix the problem if the frame itself is in good condition and air-sealed. A qualified evaluation will be used to decide if the frame should be preserved or a complete replacement would be more viable and affordable.
Q: How much does it cost to replace a fogged window IGU in Toronto?
Unit pricing varies by unit size, glass type and availability. Generally, IGU-only replacements are cheaper than window replacements. Prefer to ask to have a home assessment done and a quote given for the price that will be based on your window size and needs.
Q: Can I prevent window seals from failing?
Correct installation is the most important aspect of seal longevity. In addition, the use of non-aggressive cleaning agents close to the edges of the window, the good condition of the window frame, which does not mechanically stress the window unit, and the quality of the window and its quality spacer systems and dual-seal construction all extend the life of the IGU.
Q: Are some window brands or types more resistant to fogging?
Yes. Windows with warm-edge spacer systems (using non-metal or composite spacers rather than aluminum) suffer less edge thermal stress and are likely to have a longer window seal life. Check on the windows that have dual sealing and desiccant system of extended life. Your Toronto installer can tell you which of these products have the longest lifespan for Toronto’s climate.