There are several signs that you might need new windows:

1. Drafts: If you feel a draft coming through your windows, it could be a sign that the seal around the window is failing and needs to be replaced.
2. Condensation: If you notice condensation forming between the panes of glass in your windows, it could be a sign that the seal has failed and the window needs to be replaced.
3. Difficulty opening and closing: If your windows are difficult to open or close, or if they stick when you try to move them, it could be a sign that they need to be replaced.
4. Noise: If you hear a lot of outside noise coming through your windows, it could be a sign that they are not adequately insulating your home and need to be replaced.
5. Age: If your windows are more than 20 years old, it may be time to consider replacing them. As windows age, they can become less energy efficient and may need to be replaced to maintain the comfort and efficiency of your home.

If you are experiencing any of these issues with your windows, it is a good idea to have them inspected by a professional to determine if they need to be replaced.