The six-question diagnostic behind the tool, the thirty-second alcohol-wipe protocol that decides the diagnosis in nearly every case, the three-stage failure progression and what each stage means for replacement, and the four distinct verdicts that are not seal failure at all. The diagnostic I run on every homeowner phone call, ported to software.
What the IGU Seal-Failure Self-Check does, in five points:
The tool's job is to put the diagnostic in front of the homeowner before they spend three more bottles of cleaner trying to fix something cleaning will not fix. Or, when cleaning will fix it, to point them at the right tool. Either way, the honest answer is the goal.
There is a phone call I have either taken or written about more times than I can count. It starts the same way every time: I've cleaned this thing fifty times and it won't come clean. There's something between the panes. How do I get in there?
You don't. There is nothing you did wrong. The window has failed.
The IGU Seal-Failure Self-Check is the tool we built to put that diagnostic in front of the homeowner before the third bottle of cleaner. It walks you through the same six-question protocol I run on every phone call — symptom presentation, the two alcohol wipes, a pane count, an edge-pattern check, and the unit's age — and produces a verdict on what is actually wrong with the window. Sometimes that verdict is a confirmed seal failure with staging. Sometimes it is not a seal failure at all, and the tool routes you to the right place instead. Either way, the answer is honest.
This piece is the methodology behind the tool. What each step is testing for, why the alcohol-wipe protocol is decisive, what the three failure stages mean for replacement options, and the edge cases the tool routes to a glazier consultation rather than guessing. If you want the longer narrative treatment of the chemistry behind the failure, the foggy windows article is the deep reference. This piece is for the user who wants to understand why the tool asked what it asked.
A foggy window is a manufactured-component failure roughly seventy percent of the time, a surface-cleaning problem about twenty percent of the time, and an interior-humidity problem most of the rest. The alcohol-wipe protocol decides between these three in under a minute.
The misdiagnosis I want to prevent is the homeowner who has assumed for two years that they have a cleaning problem and has been escalating their cleaning chemistry — vinegar, ammonia, abrasive pads, then Magic Eraser, then commercial mineral removers — against a problem that is not on the glass at all. Some of those chemistries cause secondary damage to the window in addition to not fixing the original problem. The alcohol-wipe protocol terminates that escalation early.
The flip side is also true: roughly one in five "foggy window" phone calls turns out to be surface contamination that has been visually misread as between-pane fog. The diagnostic that protects the homeowner from a thousand-dollar replacement they did not need is the same diagnostic that protects them from buying more cleaner.
The first question the tool asks is what the fog actually looks like. The pattern itself carries diagnostic information before any tests are run.
Intermittent cold-morning fog that clears by afternoon is the signature of early-stage seal failure — desiccant still partially functional, cavity dew point fluctuating with the temperature differential. This is Stage 1.
Persistent haze present in nearly all conditions is mid-stage seal failure — desiccant fully saturated, moisture in the cavity continuously. This is Stage 2.
Milky, cloudy residue that does not move and does not condense-and-re-evaporate is the visual signature of low-E coating degradation, specifically silver-oxide damage from sustained moisture exposure on the silver layer of the coating stack. This is Stage 3, and it is the most upsetting stage to diagnose because the damage is permanent.
Dark streaks or black smearing creeping in from the perimeter is not fog at all — it is polyisobutylene (PIB) primary-seal sealant migrating out of the spacer. Different failure mode, same end-state (the unit needs replacement).
The "looked normal a year ago, getting steadily worse" pattern is early-stage seal failure caught in the progression itself.
The "only after rain or pressure washing" pattern is its own diagnostic puzzle that usually needs a glazier consultation — water intrusion through a frame defect rather than a seal-permeation issue, and the failure mode depends on whether the water is entering the cavity or just wetting the exterior in a way that triggers visible fog by temperature differential.
Symptom answer alone is not decisive, but it stages the diagnosis once seal failure is confirmed, and it routes butyl migration to its own verdict rather than mistakenly staging it as a fog progression.
The second question is the decisive one. The user takes a rubbing alcohol pad or a cloth dampened with isopropyl alcohol, wipes the outside of the glass vigorously over the foggy area, waits ten seconds for evaporation, and observes the result.
The test works because isopropyl alcohol cuts through nearly all common surface contaminants — finger oils, surfactant residue, silicone migration, light atmospheric soiling — and evaporates without leaving residue. Anything still visible after the wipe is, by elimination, not on that surface.
If the outside wipe cleared the haze, the diagnosis is surface haze and the tool routes the user directly to the Streak Diagnostic for chemistry-specific surface-contamination identification. No further questions needed; the IGU is not the problem.
If the outside wipe did not clear the haze, the contamination is on a different surface, and the tool proceeds to the inside-wipe test.
If the user could not run the test — upper-floor exterior, sealed glazing, accessibility issue — the tool proceeds with the inside-wipe and the other answers, and the diagnosis is somewhat less confident as a result.
The third question fires only if the outside wipe did not clear the haze, or was not run. Same protocol, opposite side: alcohol-dampened cloth, vigorous wipe over the foggy area, ten seconds for evaporation.
If the inside wipe cleared the haze, the diagnosis is interior humidity condensation — moisture from interior air condensing on the cold interior surface of the glass. This is not a seal failure; it is a physics-meets-humidity problem with a humidity solution. The tool routes the user to humidity-management guidance rather than to a glazier.
If the inside wipe did not clear the haze either, both exposed surfaces are clean. The contamination is between the panes. This is the moment when "your window has failed" becomes the diagnosis.
The two-wipe protocol is genuinely decisive. In the article version I have written about this — the foggy windows piece — the language is "this test eliminates the diagnostic ambiguity in essentially every case," and I stand by that. In the consulting practice, when both wipes have been run cleanly, I have not had a confirmed seal-failure diagnosis turn out to be something else in fifteen years.
The fourth question is a sanity check rather than a primary diagnostic move. The user holds a small candle, lighter, or LED keychain light against one side of the glass at night and counts the reflections. One reflection means single-pane; two means double-pane (IGU); three means triple-pane.
The reason this question exists is that single-pane windows do not have a sealed cavity and cannot have an IGU seal failure in the standard sense. The tool routes a confirmed single-pane diagnosis to its own verdict — surface diagnosis is the correct next step, not glazier replacement. Without this sanity check, a user with a single-pane window and a layer of surface etching could route through the tool and land at "your seal has failed," which would be wrong.
For the user who genuinely cannot run the candle test, the tool defaults to assuming double-pane (the most common modern configuration) and proceeds with somewhat reduced confidence.
The fifth question asks where on the window the fog is worst. Failed seals nearly always present worse along one specific edge or corner — typically the bottom edge (the most water exposure), one corner (a localized seal defect from manufacture or installation), or the south or west elevation (the most thermal cycling and UV exposure in the Northern Hemisphere). Fog evenly distributed across the entire pane is unusual and suggests advanced failure or a perimeter manufacturing defect.
This question is not strictly required to produce a verdict — the alcohol-wipe protocol carries most of the diagnostic weight — but the edge pattern increases the confidence in the diagnosis and tells the user which other windows on the house to check next. If one IGU has failed at the bottom edge from drainage problems, other IGUs on the same elevation installed at the same time are likely close behind. The edge-pattern check turns a single-window diagnosis into a check-the-rest-of-the-house warning when appropriate.
The sixth question asks how old the window is. IGU service life is governed by the desiccant — the molecular sieve in the spacer absorbs slow vapor permeation until it is saturated. The Insulating Glass Manufacturers Alliance (IGMA) publishes service-life expectations of 15 to 25 years for standard residential units in moderate climates, with shorter expectations for extreme-climate installations.
The age answer biases the confidence in the diagnosis without changing it. A five-year-old window with fog is probably a manufacturing defect or installation issue; the diagnosis is still seal failure, but the warranty conversation matters and the homeowner should not pay full price for replacement. A thirty-year-old window with fog is at or beyond expected service life; the diagnosis is still seal failure, but the failure is statistically normal and the warranty conversation is irrelevant.
The tool does not produce different verdicts for different ages because the underlying failure is the same regardless of age. What changes is the urgency, the warranty posture, and the question of whether to expect adjacent units to fail next.
The tool produces one of eight verdicts at the end of the decision tree:
Each verdict carries a "what it is" panel explaining the underlying cause, a ranked "what to do" panel laying out the appropriate next steps, and a diagnostic-notes paragraph with the field-experience caveats. For surface-haze and single-pane verdicts, the tool also surfaces a direct link to the Streak Diagnostic — the right tool for those problems, not this one.
The IGU Self-Check has honest limits worth being explicit about.
It cannot identify the specific manufacturer or batch of a failing IGU, which matters for warranty and class-action settlement coverage. Some manufacturers have had defective-batch settlements that cover free replacement; others have not. The tool routes the user to "document the failure if under 15 years old" for this reason, but cannot do the manufacturer-identification step itself.
It cannot distinguish capillary-intrusion failures from permeation failures, both of which present as the same Stage-2-style persistent haze. Capillary intrusion is moisture wicking through a microscopic seal breach driven by water-side pressure (rain, sprinkler exposure, ice-damming melt); permeation is the slow vapor-diffusion failure of an aging desiccant. The replacement answer is the same for both, but the prevention conversation differs — capillary failures often correlate with drainage problems that, if uncorrected, will fail the replacement IGU too.
It cannot identify glass-to-glass condensation in storm-window-over-primary configurations, where the apparent "between-pane fog" is actually condensation on the storm-window side facing the primary glazing. This is a humidity-and-temperature interaction that mimics seal failure visually but is not one. A homeowner with this configuration should consult a glazier; the tool routes them to inconclusive.
It cannot determine whether the failure is covered by warranty or settlement, which is the question with the most financial weight in many cases. The tool notes the conditions under which to investigate this but cannot answer it.
It cannot run on glazing the homeowner cannot reach — upper-floor exterior glass without access, glazing sealed under stucco or trim, commercial curtain-wall glazing. The two-wipe protocol requires both surfaces to be accessible. When either surface cannot be reached, the tool routes to a partial-confidence verdict and recommends professional inspection.
The tool's job is the eighty-percent diagnostic that a careful homeowner can run with their own eyes and a bottle of rubbing alcohol. The remaining twenty percent is consultation territory.
The alcohol-wipe protocol I run on every "foggy window" phone call was not invented at a desk. It came out of fifteen years of customer-service inquiries at a glass coating manufacturer, where the technical-service team had a recurring problem: homeowners describing fog patterns that could be three different failures, and no way to triage over the phone without an in-person visit. The two-wipe sequence — outside first, inside second, both decisive — became the protocol that resolved roughly ninety percent of the calls without a service visit.
The six-question structure of the tool is the version of that protocol that adds symptom-pattern staging (for the post-confirmation severity question), pane-count sanity-checking (for the single-pane edge case), edge-pattern check (for adjacent-window warnings), and age-and-history (for warranty posture). None of those steps are strictly necessary for the alcohol-wipe diagnosis itself. They are the steps that turn a yes-or-no answer into a useful answer.
The "honest about what cleaning can't fix" voice that runs through the rest of the site is operationalized in this tool more directly than in any other one. When the diagnosis is surface haze, the tool tells the user clearly that this is the better problem to have and routes them to the cleaning tool. When the diagnosis is humidity, the tool tells them clearly that the window is fine and the air is the issue. When the diagnosis is confirmed seal failure, the tool tells them clearly that cleaning will not fix this and lays out the actual options with pricing.
The tool is, in a meaningful sense, the article's voice in interactive form. The article tells the homeowner the diagnosis at the end of a 2,900-word piece. The tool tells them the diagnosis in five minutes of clicking, and it works whether or not they read the article first.
Easton Giordano is part of the Giordano Inc. editorial team and covers the Pacific Northwest and West Coast editorial beat for Window Washing Guide. Editorial content is researched and reviewed in collaboration with the Giordano Inc. editorial team and informed by interviews with practicing window-washing operators in the region, plus published trade and materials-science references.
Easton Giordano is part of the Giordano Inc. editorial team and covers the Pacific Northwest and West Coast editorial beat for Window Washing Guide. Editorial content is researched and reviewed in collaboration with the Giordano Inc. editorial team and informed by interviews with practicing window-washing operators in the region, plus published trade and materials-science references.