Inside or outside?
Clean both sides of the glass. If the haze is still there, it's between the panes. Condensation on the room side in winter is usually indoor humidity, not a failed seal.
Why it happens
A double-pane window is a sealed unit with a spacer and a seal around the edge. Sun, heat, and years of weather break that seal down. Moist air leaks in and fogs the glass from inside.
What fixes it
The lasting fix is a new sealed unit. We measure your existing unit, order a new one to size, and install it in your current frame. See foggy double-pane glass replacement.