When it comes to replacing the windows in your home you are basically left with two choices; new construction windows or retrofit windows. While there are a number of pros and cons to each type of window, retrofit windows are typically much simpler and less expensive to have installed. Unfortunately, you may not always have a choice when it comes to the type of windows you choose. If your home is equipped with original vinyl windows, for instance, retrofits are not a plausible solution when it comes to choosing the type of replacement window to use.
Retrofit windows are designed with the intention of removing the interior and middle stops in order to rest the new insert on the outer stops of the existing frame. With original vinyl windows, these parts are typically molded into the frame, making the intended installation process of retrofit windows nearly impossible.
While force-fitting the window insert might be an option in some cases, it is not recommended because doing so could damage the frame as well as the insert, and will almost certainly void any warranty your new replacement windows might have. If your home is equipped with original vinyl windows that need to be replaced, your best option is likely to be new construction windows instead.