Yes, you should replace all windows at once. Window replacement is a big job, but it's best to do it all at once. That way, you'll only have to go through the hassle and expense of replacing windows once, and you'll also be sure that your home will be more energy-efficient all year round. There are many factors to consider when choosing new windows, such as the climate in your area and the type of window frame you prefer. But by working with a qualified window installer, you can be sure that you're making the best decision for your home.