Cleaning cannot fix a foggy double-pane window, because the fog is not on a surface anyone can reach. It is condensation sealed between two panes of glass, behind a failed edge seal. No cleaner, no pure water, no squeegee touches it. Here is how it fails, how to confirm it, and what it costs to fix.
A modern window is not one piece of glass. It is an insulated glass unit: two panes held apart by a spacer bar, with the gap sealed and filled with dry air or argon. Count the surfaces from outside in and you get four. Surface 1 is the outdoor face. Surface 4 is the one in your living room. Those are the only two that anything can touch. The haze in a fogged window lives on surfaces 2 and 3, inside a sealed cavity usually a half inch wide, and there is no opening into it. Deionized water does not reach it. A razor does not reach it. Neither does vinegar, ammonia, a magnetic cleaner, or anything sold in a spray bottle as a fog remover. If the haze is between the panes, the unit has failed, and the fix is glass, not cleaning. The rest of this page is how it got there and what your options actually cost.
The edge seal is two layers. The primary seal is a thin bead of polyisobutylene, often only a third of a millimeter thick, pressed between glass and spacer. That black rubber is the real vapor barrier. The outer seal, silicone or polyurethane, is structural. Inside the spacer sits desiccant, 3A molecular sieve beads that absorb the trace moisture sealed in at the factory. The unit does not fail the day it starts leaking. It fails the day that desiccant is full. Getting there is a pumping problem. Gas in the cavity expands when sun heats the glass and contracts overnight. A south-facing pane in a dark frame can run 140 to 160 degrees F on an August afternoon here and sit below 20 degrees F on a January night. That swing works the seal thousands of cycles a year, and every cycle draws a little humid air past a weak spot. Ten to twenty years of it saturates the desiccant. Then the cavity fogs.
Wipe the inside of the glass with your hand. Wipe the outside. If the haze is gone, it was never a seal problem. Condensation on surface 4, the room side, is an indoor humidity problem, not a window defect. Condensation on surface 1, the outdoor face, is dew, and it is the sign of a window doing its job: a good low-E unit keeps the outer pane cold enough to drop below the morning dew point. That is common on Treasure Valley mornings in April and October and it burns off by nine. If haze survives both wipes, it is between the panes. Two more tells confirm it. Seal-failure fog usually moves with the sun, thin or gone by mid-afternoon on a hot day and back by morning. And it is uneven, heavier at the bottom edge where water pools, often with a visible tide line or white mineral streaking near the spacer.
Defogging is real, and it is not what most people picture. A tech drills one or two small holes through the outer pane, sprays a cleaning solution into the cavity, lets it drain, then fits a one-way breather vent in the hole. Cost runs roughly $75 to $200 per window. Be clear about what you get. You get some clarity back, usually not all of it. You do not get the seal back, the argon back, the desiccant back, or the original R-value back. The unit is now deliberately vented, so it will breathe outdoor air for the rest of its life, and haze can return within a season or two in a humid stretch. It voids whatever glass warranty remained. And it does nothing about mineral staining. Once condensation has cycled on surfaces 2 and 3 long enough, dissolved calcium and silica etch the glass permanently. Cleaning that cavity does not remove etched glass.
The frame, sash, hardware and weatherstripping are almost always fine. What failed is the sealed glass unit inside them, and on most vinyl and clad windows a glazier can pull the stops and swap just that unit. Budget roughly $200 to $600 for a common double-pane low-E argon unit, and $700 to $1,200 for oversized, tempered, obscure, or grid-between-glass units. A full replacement window installed generally starts around $600 and climbs fast. Before you call anyone, check the corner of the glass for an etched date code or manufacturer stamp, and look for a date stamped into the aluminum spacer. Many manufacturers warrant the seal for 10 to 20 years, and a fogged unit inside that window can be free glass. Also count the whole elevation. If two units on the west side have gone, the rest are the same age with the same sun on them, and pricing them together usually beats three separate trip charges.
We do not fix seals. We do not sell defogging, and we will tell you on site if what you are looking at is a dead unit so you stop paying anyone to scrub it. Worth knowing: cleaning a fogged window often makes it look worse, because once surfaces 1 and 4 are truly clear, the milk between the panes is the only thing left to see. If you are replacing a unit within the next couple of months, tell us and we will drop those panes from the count, which lowers your bill since our pricing runs by pane count starting at $199. One real caution on the exterior side. Normal window cleaning does not kill a seal, but high pressure aimed at a glazing bead can drive water into the frame. Our house washing is soft wash at about $0.18 per square foot and stays under roughly 500 PSI. The 3,000-plus PSI wand belongs on concrete, not near glass.
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Still wondering about something? Call or text us at (208) 453-6760.
No. The cavity is sealed on all four edges by the primary seal and the spacer, with no access point. Every product marketed as a between-the-panes cleaner either works on surface 4 only, or requires drilling the glass. If a company quotes you a price to clean the inside of a sealed unit without opening it, they are either misunderstanding your window or selling you nothing.
Less than most people assume. When argon escapes and is replaced by air, a typical unit moves from roughly U-0.30 to U-0.35, maybe a 10 to 15 percent hit on that window's insulating performance. On one or two windows in a house that is dollars a year, not hundreds. The real costs are the view, the appraisal and inspection notes at resale, and the permanent mineral etching that develops if you leave it for years.
No, that is the opposite signal. Exterior dew forms because a good low-E unit keeps the outer pane cold, letting it drop below the dew point on a clear, calm morning. You will see it most on spring and fall mornings in the valley and on the sky-facing side of the house. It wipes off, it burns off with sun, and it means the glass is insulating well.
That is humidity, not glass. Target 30 to 40 percent indoor relative humidity in winter, and drop below 30 percent when outdoor temperatures fall under about 10 degrees F. A $15 hygrometer tells you where you stand. Run bath fans 20 minutes after showers, vent the dryer outside, and check that a whole-house humidifier is not set to a summer number in January. No service call needed.
Because they take the most thermal cycling. Boise sits near 2,700 feet with roughly 200 sunny days a year, big day-to-night temperature swings, and strong UV. South and west glass gets the longest, hottest exposure, so the seal gets worked hardest and the sealant degrades fastest. North-facing units on the same house frequently outlive them by years. It is also why a lot of Treasure Valley homes built in the 2004 to 2008 boom are fogging now, right at the 18 to 22 year mark.
Usually yes, but skip the dead ones. The other panes still get dirty, and frames, tracks and screens still need attention regardless of what the sealed units are doing. Tell us which windows are fogged when you book. We take them out of the pane count rather than charging you to clean glass that will look hazy anyway, and we will note the ones we think are on their way out.
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