Thermos needs replacing? 7 signs to check yourself before calling
A 5-minute inspection that could save you thousands of dollars
Do you suspect that your windows are not performing as well as they used to, but you don't know if the problem is with the thermal panes or something else? Before requesting a quoteTake a quick tour of your home with this diagnostic checklist.
A faulty thermos doesn't always show obvious signs. Some symptoms are subtle and appear gradually, to the point that we get used to them without realizing how much they affect our comfort and our wallet.
Here are the 7 of the most reliable signs Our experts use these tests to diagnose sealed glazing that has lost its airtight seal. Take 5 minutes to check them at home — the results will likely surprise you.
💨 Fog or condensation between the windows
This is the most obvious and well-known sign. If you see condensation, droplets, or even small whitish spots inside of the double glazing (and not on surfaces that you can wipe clean), the sealing gasket has failed.
🔍 How to check: Wipe both sides of the glass thoroughly. If condensation persists, it is trapped between the two panes — therefore impossible to clean.
🌫️ Glass warm to the touch in direct sunlight
On a sunny day, a high-performance double-glazed window with argon gas and a Low-E coating remains relatively cool to the touch on the inside, even when the sun is beating down. If your window is burning hot to the touchThis means that the thermal barrier is no longer working and that the heat is being transferred directly into your home.
🔍 How to check: Around 2-4 pm, touch the inside of a south- or west-facing window. If it feels uncomfortably hot, compare it to a newer window — the difference will be striking.
🌡️ Temperature difference between rooms
If some rooms are consistently warmer in summer or colder in winter than the rest of the house, your double-glazed windows are likely the culprit. Faulty glazing allows outside temperatures to pass through much more easily.
🔍 How to check: Place your hand 10 cm from the glass on a hot or cold day. If you can clearly feel the outside temperature, the thermos is no longer working properly.
💸 Energy bills that increase for no reason
Compare your Hydro-Québec bill this winter (or spring) to the same period last year. If it has increased without any change in habits or rates, your windows are probably letting in heat — or letting in summer heat.
🔍 How to check: Log in to your Hydro account and compare your kWh consumption over 12 months. An increase of 10-30% without an obvious cause is a warning sign.
🎨 Stains, deposits or permanent residues
Over time, the moisture trapped inside the thermos leaves mineral residue. You will see the appearance of whitish spots, streaks or a permanent film which doesn't disappear, no matter how you clean. These are deposits between the panes of glass.
🔍 How to check: Look at your window against the light. The deposits become much more visible when the light passes through.
🍃 Drafts near the windows
If you feel a draft when you pass your hand near the window (without touching the frame), it means the glazing is no longer providing proper insulation. Caution: if the draft comes of the frame outlineIt's more of a structural insulation problem, not a thermos problem.
🔍 How to check: Light a candle and hold it 5 cm from the glass. If the flame flickers in the center of the glass, the thermos is the problem.
☀️ Discoloration of furniture and floors
A thermos in good condition with a Low-E coating blocks up to 95% of UV rays. If your furniture, carpets, wood floors, or curtains are covered in UV-resistant material, protect them from UV rays. lose their color Near the windows, it means the protective film is no longer working.
🔍 How to check: Move a cushion or picture frame a few months ago and look at the difference in color compared to the area exposed to the sun.
How many signs did you identify?
0 to 1 sign
Your thermoses are probably in good condition. Continue to check them annually.
2 to 3 signs
Some thermos units are starting to show signs of wear. A professional inspection is recommended.
4 or more signs
Your thermoses are faulty and costing you a lot of money every month. Replacement is strongly recommended without delay.
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Good news: no need to change everything
If your window frame is still sound (PVC, wood, or aluminum in good condition), you only need to replace the sealed glazing. It's a quick, clean, and much less expensive solution than replacing the entire window.
⏰ Don't wait for the problem to get worse
A faulty thermos won't fix itself—on the contrary, the problem worsens over time. Trapped moisture leaves permanent deposits on the glass, energy efficiency continues to decline, and your utility bill increases every month. The longer you wait, the more the inconvenience and costs accumulate.
Having your thermoses assessed as soon as the first signs appear allows you to take action. before the problem becomes urgentand to benefit from a quick installation without having to deal with delays during peak season.
✅ Summary: The 7 signs
1Fog or condensation between the windows
2The glass was burning hot to the touch in direct sunlight.
3Rooms heated or cooled unevenly
4Hydro-Québec bill on the rise
5Stains or permanent deposits on the glass
6Air current in the center of the glazing
7Discoloration of furniture and floors
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Doubts about the condition of your thermoses?
Our experts inspect your windows and give you an honest diagnosis.
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Thermos Inc. Change
Over 20 years of experience
Warranty up to 10 years
Fast service in Montreal and Laval
