Q: About 10 years ago, I replaced all the windows in my house with vinyl-framed, dual-pane insulated glass. I don’t think they were top-of-the-line products. The two swing-out windows in the kitchen appear to have some etching or scratching that has gotten worse. That side of the house is usually in the shade, so these windows don’t get much sun exposure, and the cloudiness doesn’t seem to be affected by the air temperature or weather. I have tried cleaning the glass inside and out, but the etching appears to be on the glass facing the air gap between the panes. What would cause this? Is there anything that can be done to fix this?

A: John Weaver, who handles customer service inquiries for Circle Glass and Mirror in Fairfax, Va., looked at the pictures you sent and said the cloudiness is definitely condensation, which forms inside dual-pane glass units once the desiccant in the spacer between the panes becomes saturated. Dual-pane units are made with a thick sealant around the edges, but the seal is never perfect. Over time, warm air, which holds more moisture, seeps into the gap between the pieces of glass and releases that moisture when it cools. The desiccant absorbs it, keeping the glass clear – until the desiccant stops working. At that point, the only remedy is to replace the glass units.

The etching or scratch-like marks you see are caused by a failure of a low-e coating that was applied to the glass, Weaver said. Low-e, for “low emissivity,” refers to a microscopically thin coating of metallic particles that reflect some wavelengths of light while allowing most of the visible wavelengths to pass through. Low-e coatings keep out most ultraviolet wavelengths, which helps keep furnishings from fading. Depending on the coating and which glass surface it’s applied to, low-e coatings can also reflect infrared wavelengths toward the outside or the inside, keeping homes warmer in winter or lightening the load on air conditioners in summer.

Low-e coatings can be “hard coat,” meaning they were sprayed onto the molten glass as it was formed into sheets, or “soft coat,” applied later in a vacuum chamber. The hard-coat process allows the glass to be cut and tempered, and it forms a strong enough bond that window manufacturers can add features such as between-the-pane blinds. But the soft-coat process, while more fragile, results in better energy savings.

“Some of the older low-e coatings have a hard time sticking to the glass for more than about five to seven years,” Weaver said in an email. “It is a totally organic failure, and it is not atypical of soft-coat low-e’s. If you have ever had a pair of sunglasses where the coating has begun to peel off, it’s the same exact thing.” As you discovered, the coating can’t be cleaned, or even scraped off, because it’s between the two panes of glass on the inside of the unit.

To see clearly out of your windows, you don’t need to replace the entire set of windows, just the glass units that look cloudy. Cloudiness is a visual issue; it doesn’t make a significant difference in energy efficiency, so if the cost of replacement is too much for your budget, you can delay until your finances are in better shape.

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You would need to call around to glass companies – not window-replacement companies – to get cost estimates in your area. In the Washington area, replacement dual-pane units from Circle Glass generally price out around $75 to $125 for materials (depending on size, coating and whether it has grids), plus $25 to $50 for labor when a homeowner brings in the framed sash for measurements and returns around 10 days later to have the new units installed, Weaver said. The company can also make two trips to a house, once to measure and again to install. Labor with that option starts at $235 for one pane, plus $50 to $75 for each additional pane.

If you opt to replace the glass in your kitchen windows, choosing low-e glass still makes sense in terms of energy efficiency and comfort. But Weaver cautioned that the newer coatings might change the color of the glass, which could alter the tones that you see when looking out. He said it is almost impossible to match the color of new low-e glass with older low-e glass, “so if that is a concern, it might be best to just put in clear glass in that particular space,” especially because it’s on the shady side of the house, where blocking heat from sunlight in summer is less of an issue.

Weaver said that, based on what he has been told, “the newer low-e coatings are much more durable and more securely bonded to the glass than the older-generation low-e’s.” He said the sealant on the glass should last five to 10 years, and the coatings should outlast that by several years.

On new windows, manufacturers offer warranties against cloudiness and other defects that stretch for many years, so it might be worth digging out the paperwork for your windows, if you still have it. Milgard, for example, offers a “lifetime” warranty for as long as the purchaser lives in a house; it also covers 10 years from the date of installation if the house sells. But built into the warranty calculation is the overall cost of the windows, which is much higher than just for the glass units, and a gamble that most people don’t stay in the same house for a lifetime. If replacement glass units have a warranty, it’s unlikely to last for more than 10 years.