If your windows are no blame for condensation– not a ventilation or moisture issue — there are some sure signs they need to be replaced: 1) Frost and condensation are a constant issue. 2) It’s noticeably colder in the area of the window. 3) You can see mold or decay around the windowsill or frame. 4) The windows are jamming. 5) Condensation or frosting is happening between windowpanes. That means the airtight seal is broken. If that’s the case, then your only solution is replacing the entire window.