Knowing when to replace your windows can depend on a variety of factors. Here are some signs that it might be time for a replacement:

1. Drafts and Air Leaks: If you feel drafts or notice that your home is not as energy-efficient as it used to be, your windows may be letting air escape or enter. You can check for drafts by holding a candle near the edges of the window and seeing if the flame flickers.
2. Condensation Between Panes: If you see condensation or fogging between the panes of your double- or triple-pane windows, it usually means the seal has failed and the window needs to be replaced.
3. Difficulty Opening or Closing: If your windows are hard to open or close, or if they don’t stay in place, it could indicate problems with the window mechanisms or frame, which might require replacement.
4. Visible Damage: Look for physical damage such as cracked or broken glass, rotting frames, or deteriorated sashes. These issues not only affect the appearance but can also impact the window's performance.
5. High Energy Bills: If your energy bills are rising and you’re not sure why, old windows might be to blame. Modern windows are designed to be much more energy-efficient than older models, and upgrading can help reduce heating and cooling costs.
6. Noise Issues: If outside noise seems louder than it used to be, your windows might not be providing adequate insulation. Newer windows often have better soundproofing features.
7. Age of Windows: Windows typically have a lifespan of 15 to 30 years. If your windows are approaching or surpassing this age range, it might be a good idea to start considering replacement.
8. Peeling Paint or Rotting Wood: For wooden windows, peeling paint or rotting wood can be a sign of age or water damage. While some of these issues can be repaired, extensive damage might warrant replacement.

If you notice any of these signs, it’s a good idea to consult with a window professional who can assess the condition of your windows and recommend the best course of action.