If your home was built in the 80’s or 90’s you should consider removing the old frames:

Most existing wood window frames have very little or no insulation between them and the frame of the house. Having high performance windows installed on such frames is really only doing half the job, as cold air will still penetrate your home around the wood frame.

You will lose a significant amount of glass area by having a new vinyl window installed on an existing wood frame.

Existing frames are not shimmed to support your new vinyl window, which will cause it to sag in the future, resulting in problems with drafts and leaks with you new window.

If you choose to have your new windows installed “Brick to Brick” (or siding to siding) you will have eliminated the 3 problems stated above. You will also eliminate the bulky look of the aluminum capping that is used cover over wood that remains.