Fog Between Window Panes: Replace the Glass or the Window?

Find which surface is wet

Wipe the room-side glass with a clean cloth. If the haze clears there, you are looking at interior surface condensation, not proof of a failed sealed unit. Exterior dew can also form on a cool pane. Check the outdoor surface only where it is safely accessible; do not lean out or climb unsafely to settle the question.

Andersen distinguishes condensation between glass panes from condensation on an accessible surface and identifies between-pane moisture as a sign of seal failure Andersen: Window condensation.

A cloud that remains inside the glass, droplets within the cavity or a persistent internal stain supports a glazing-service enquiry. Dirt or a film on one surface can look similar in certain light. Photograph the condition at different times and note whether either surface can be cleaned clear. Do not scrape with a blade to test it.

Glass, sash and complete window are different quotes

Andersen specifies replacement sashes or panels for many of its products rather than separate glass replacement, while noting some older direct-set exceptions Andersen: Glass replacement and sash options.

Ask the manufacturer or a qualified glazing service whether your sash can be reglazed and whether a factory replacement sash is available. Glass thickness, coatings, spacer dimensions, safety-glazing requirements and setting details must match the application. This is not a matter of ordering two pieces of ordinary glass cut to the visible opening.

A clear new sealed unit can be a sensible repair when the surrounding frame, sash, hardware and water management are in good condition. If the sash is deteriorated, a replacement sash may make more sense. If the main frame leaks, is distorted or has extensive decay, pricing only glass can leave the expensive problem untouched.

Ask what is included and what remains

Renewal by Andersen's replacement comparison distinguishes work that retains the existing frame from full-frame removal Renewal by Andersen: Full-frame versus insert replacement.

Request a written scope identifying which components remain, the glass specification, finishing work and warranty on the repair. Check the original product warranty before paying for replacement. Keep labels, purchase information and photographs; do not assume that glass coverage includes every labour or trim cost.

A service advertised as defogging may improve appearance without replacing the original sealed unit. Ask exactly what is done and what thermal or seal performance is restored and warranted. A clear view alone does not demonstrate that the original glazing performance has returned.

Use the visit to inspect, not automatically replace everything

List any hard operation, loose locks or rainwater entry separately. A crank fault is not evidence that every pane needs replacement. Conversely, full-frame replacement may be appropriate when several parts of the opening have failed. The useful quote explains why its scope matches the observed condition.