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  • Energy-efficient window installation on a residential home

Fogged or Cloudy Glass Between Panes

Fogging between the glass panes — cloudiness, streaking, or moisture droplets visible between the layers that do not wipe off from either glass surface — is the most common residential window complaint and one of the clearest-cut diagnoses. This condition has exactly one cause: the edge seal of the insulated glass unit (IGU) has failed, allowing moist air to enter the sealed space between the panes. Over time, the moisture evaporates and deposits mineral salts on the interior glass surfaces, which appears as whitish or gray permanent hazing. The condition progresses — it does not self-correct. Once a seal fails, the insulating gas fill (argon or krypton) is also lost, and the window's thermal performance is reduced to that of a non-gas-filled unit. The appropriate response depends on the frame condition. If the frame is structurally sound — no rot, no visible warping, hardware functions correctly — an IGU-only replacement is the cost-effective fix. An installer removes the glazing stops inside the sash, slides out the old IGU, and installs a new unit manufactured to the exact sash dimensions. Cost is $150–$350 for residential sizes depending on the glass package specified in the replacement. If the frame is deteriorating, caulk is failing at the exterior, or the window is 25+ years old with any hardware issues, full window replacement is the better investment. Check your manufacturer warranty documentation — IGU seal failures within the warranty period may have the glass covered at manufacturer cost.

Drafts — Locating and Fixing the Source

A draft at a window you can feel on your hand when the window is closed and latched has one of three origins: failed weatherstripping at the sash-to-frame junction, a gap in the exterior caulk joint between the window frame and the adjacent siding or trim, or a broken or open balance slot that creates a air path at the top or side of the sash. Locating the source is the first step. On a cold day with wind, hold a stick of incense or a damp hand along the perimeter of the closed window, starting at each corner of the sash. Draft from sash weatherstripping failure shows up at the sash edges — consistent air movement along the full height of the sash side, or at the meeting rail on a double-hung. Draft from a failed exterior caulk joint shows up at the perimeter of the entire window frame, not just the sash edge. Draft from a failed balance slot shows as air at the top of the sash where the balance housing sits. Each has a specific fix: weatherstripping replacement at the sash perimeter (a homeowner-accessible repair), exterior caulk removal and replacement at the frame joint, or balance mechanism replacement. Attempting to caulk the exterior joint without first addressing weatherstripping failure will reduce drafts only partially — both conditions can coexist and both need to be addressed for full resolution.

Hard-to-Operate Sashes and Mechanisms

Vinyl windows that have become difficult to open and close over time are experiencing one of three conditions: track debris accumulation, balance mechanism failure, or frame distortion. Track debris — grit, paint overspray, insect material — accumulates in the sash channels over years and creates friction. The fix is cleaning with a vacuum and damp cloth followed by lubricating the track with a dry silicone spray (do not use petroleum-based lubricants in vinyl tracks — they attract more debris). Balance mechanism failure is the cause when the window feels fine moving in one direction but resists in the other — a sign that the spring tension in the balance is insufficient. The fix is balance cartridge replacement as described in the Maintenance section. Frame distortion causing operation difficulty is the most serious condition and occurs when the rough opening settles unevenly, racking the window frame out of square. If the frame is visibly twisted when you sight down it, or if the sash binds specifically at one corner, frame distortion is likely. This is a structural issue in the rough opening, not a window issue — shimming corrections may restore operation but a larger settlement issue should be investigated. For casement windows, difficult cranking usually indicates crank mechanism wear or hinge corrosion. Lubricate the hinge arms with white lithium grease and the crank mechanism with dry silicone. If the mechanism is stripped or broken, replacement crank operators are available from most manufacturers for 10–15 years after window production.

Interior Condensation and Frost at Frame Edges

Interior surface condensation — water droplets on the room-side glass surface — is frequently misdiagnosed as a window failure when it is almost always a humidity and temperature management issue. In Utah, forced-air heating drives indoor relative humidity to 15–25% in winter, which is below the range where condensation typically forms on modern high-performance glass. However, in kitchens and bathrooms where humidity spikes, and on older windows with lower interior surface temperatures (U-factor 0.40 or above), condensation can occur when indoor humidity is briefly elevated. The fix is ventilation control — ensuring range hoods vent to the exterior, bathroom exhaust fans run during and 15 minutes after showers, and a whole-house humidifier is set to the appropriate winter setpoint (30–35% relative humidity in Utah winter conditions). Upgrading windows to higher-performance units reduces condensation risk by raising the interior glass surface temperature, but it does not eliminate the underlying humidity source. Frost at the frame perimeter — ice forming at the bottom corners of window frames in very cold weather — indicates a thermal bridge at the frame. Metal window spacers conduct heat from the interior glass perimeter to the cold exterior, and when interior humidity is above 20%, condensation freezes at these spots. Warm-edge spacers in the IGU significantly reduce this effect. On older windows with aluminum spacers, frost at corners in cold weather is expected and is not a failure — it is a performance limitation of that generation of glass technology.

Common Questions

My window is fogged on just one pane — is that different from fogging between panes?
Yes, completely different. Fogging on the interior room-side surface is temporary condensation from indoor humidity and clears as humidity normalizes — this is a humidity management issue, not a window failure. Fogging on the exterior surface clears as the sun warms the glass — this is harmless and indicates high-performing glass. Fogging that is permanent, visible between the glass layers, and does not wipe off from either surface is IGU seal failure and requires glass unit replacement.
My window is drafty but the glass is not fogged — do I need full replacement?
Not necessarily. Drafts at a window without fogging indicate weatherstripping or caulk failure — both of which are maintenance repairs on otherwise functional windows. Before replacing windows based on drafts, have the weatherstripping and exterior caulk inspected and replaced. In most cases this resolves the draft for $50–$150 in materials and a few hours of work, extending the window's useful life significantly.
There is water pooling on my interior window sill every morning in winter — what causes this?
Water pooling on the sill is condensation draining from the interior glass surface. The root cause is indoor humidity combined with a cold glass surface. Utah's winter HVAC systems produce very dry indoor air, which means visible condensation on windows is usually from a localized humidity source nearby — a humidifier set too high, a large aquarium, or proximity to the kitchen. Reduce humidity at the source and improve ventilation. If the sill itself is showing water damage or mold, the condensation has been ongoing long enough to require sill repair.
My window hardware is failing — latch does not engage, crank is stripped — should I replace the whole window?
Hardware replacement is typically far less expensive than window replacement and is the right answer when the frame and glass are otherwise sound. Most window manufacturers stock replacement hardware for 10–15 years after a model leaves production. Obtain the window brand and model number from the label inside the sash or frame, call the manufacturer's parts line, and order the specific component. The latch assembly and crank operator are the two most commonly replaced hardware items. Replacement is usually a 30–60 minute job.
My windows sweat on the exterior in the morning — is something wrong?
Exterior surface condensation that clears as the morning sun warms the glass is normal and actually indicates high-performance glass. The glass is cold enough (well-insulated from indoor heat) to fall below the exterior dew point on cool, humid mornings. This is more common with triple-pane and high-performance double-pane glass than with older, less-efficient windows. It is not a defect.

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