Why Do My Windows Fog Up on Marine Layer Mornings
Ten dollars for a fan timer against several hundred for a replacement glass unit is the arithmetic to settle before anyone orders anything. Wet glass on a window in Carlsbad is a dew point question first and a defect question second, as the notes at vinyl windows carlsbad fretboard summit describe. The location of the moisture decides the diagnosis, so start by finding which surface it sits on.
Why the glass gets wet at all
Condensation forms when a glass surface is cooler than the dew point of the air touching it. That is the whole mechanism. Nothing leaks and nothing fails. Water leaves the air and lands on the coolest surface in the room, and glass is usually that surface.
The marine layer changes the numbers
Humid coastal air from the marine layer raises the dew point, so moisture shows up on glass more easily near Carlsbad State Beach, Agua Hedionda Lagoon and Batiquitos Lagoon than it does inland in San Diego County. A cool morning with low cloud can put a film on a slider or picture window that is gone by ten o'clock.
Moisture on the room side
Moisture on the inside surface usually comes from indoor humidity. Cooking, showers and sleeping occupants all put water into the air overnight. The cold edge of a double hung or casement sash is where it lands first. Run the bath and kitchen exhaust fans, and keep air moving near the glass, with curtains open and furniture pulled back from the sill. That lowers interior condensation without touching the window.
Moisture on the outside
Moisture on the outside surface is common on cool, humid mornings. It often means the glass is insulating well, because the outer pane stays cool instead of being warmed from the room. It is not a leak. Wipe it or wait for the sun. Newer frames with warm edge spacers also keep the glass edge warmer than older aluminum spacers, which cuts condensation along the bottom edge.
Fog between the panes
Fog or haze between the two panes is a different problem. It means the edge seal has failed and moist air has entered the sealed space of the insulated glass. Wiping does nothing, because the film is inside the unit. Check by running a finger across both outer faces. If neither face is wet and the haze stays, the seal is gone. The repair is a replacement glass unit, or a whole new sash when the frame is worn or the unit cannot be sourced. A sealed double pane unit that has fogged will not recover, and the sooner it is measured and ordered, the sooner the view is clear again.