Low-E glass is standard on most windows installed in Minnesota today, and homeowners ask whether cleaning can damage it. For most windows the answer is no. For one type of coating, it matters how the glass is cleaned. Here is how to tell the difference.
What Low-E glass is
Low-E (low emissivity) glass has a microscopically thin metallic coating that reflects heat. In winter it helps keep heat inside; in summer it helps keep it out. You cannot see it, but it does a lot of work for your heating and cooling bills.
Where the coating sits
Window makers number the glass surfaces from outside in. On a double-pane window, surface 1 faces outdoors, surfaces 2 and 3 face each other inside the sealed space, and surface 4 faces your room.
- Coatings on surface 2 or 3 are sealed inside the glass unit (the same seal that causes foggy windows when it fails). This is where most Low-E coatings are. Nothing touches them during cleaning, so the window cleans like any other glass.
- Coatings on surface 4 (room side) are used on some newer, higher-efficiency windows to add extra insulating value. These coatings are durable, but they are exposed, so they need gentler cleaning.
How to tell if you have a room-side coating
- Check the paperwork or the glass. Window orders, manufacturer labels and stickers often list the glass package.
- Try the flame test. Hold a lighter or match close to the glass at night and look at the reflections. You will see one reflection per surface. A reflection that looks a different color from the others is coming off a coated surface. If the odd-colored reflection is the one closest to you, the coating is on the room side.
- Ask your window installer. They can tell you from the model or order.
How to clean a room-side Low-E coating
- Use a soft cloth or squeegee with a mild, ammonia-free glass cleaner or soapy water.
- No razor blades and no scraping.
- No abrasive pads, steel wool or gritty cleaners.
- Do not use harsh chemicals, and rinse off any cleaner you are unsure about.
That rules out some hard water stain and debris removal methods that are fine on uncoated glass, such as scraping off paint or construction residue. If a coated room-side surface has heavy deposits, talk to the window manufacturer about what they allow.
Will cleaning remove a Low-E coating?
Not with normal, gentle cleaning. Coatings sealed inside the glass are completely protected. Room-side coatings can be scratched by blades and abrasives, which is why technique matters there.
What we do
When you book, tell us if your windows have a room-side coating. That way the crew knows ahead of time which surfaces should not be scraped, and we can talk through any stains or construction debris on that glass before we start.
Related questions
- How much does window cleaning cost?
- Hard water stains on windows: what comes off and what does not
- Foggy windows between the panes: what a failed seal means
- French pane and grid windows: what to know before they are cleaned
Want us to take a look?
We clean windows across Lake Minnetonka and the west metro. Get an instant estimate, call (612) 770-8221, or see our window cleaning packages and prices.