A double-hung window features two operable sashes, meaning it has an upper window part and a lower part that can both open to let in fresh air. A picture window has one fixed glass panel that doesn’t open. Double-hung windows cost about $200 to $2,500, while picture windows cost about $200 to $1,900.

If the existing frame around the window sash is completely structurally sound, it's possible to save money by swapping out the sash for a new one instead of getting a new window. Keep in mind that it will be necessary to find a new sash that perfectly matches your existing window structure. In general, consulting a window pro to help you find the right match is the best way to ensure you're doing this project correctly.

There are many signs to look out for that tell you it’s time to replace a double-hung window. If the window is drafty and inefficient, you may need a new window to block out air leaks and keep your utility bills from skyrocketing. Other signs that it’s time to replace a window include foggy glass, soft or broken window frames, or window sashes that won’t open or close easily.

In short, it depends. After 20 years, the glass in your windows is less energy efficient, which can cause increased electricity bills. You might also see signs of water damage or natural wear and tear over the years. However, with proper maintenance, some window frames can last up to 50 years, so you may only need to replace the glass to save on energy. 

At the same time, window replacement is a major investment, so replacing the glass in rooms most impacted by outdoor temperatures is one way to avoid going all-in to replace your windows.