Doors and Windows - D/H window frame installation

i want to install a 27x16 double-hung window frame from the outside of the house. i saw on a fixit show on tv that these frames need to be shortened a little so they will fit into the opening if they are replacments for an original. otherwise the frame will not be true vertical but will tilt a little bit. how do i shorten the wood frame that comes preassembled from the manufacturer. also how much do i take off - half inch or what? thanks

Have no idea what you saw on TV, and most of it is "entertainment" and very little on facts or skill, so take it with a grain of salt. That stuff about shortening the height to keep the window from tilting to one side makes no sense whatsoever.

You need the rough opening required for your window, and then get that size opening in your wall......and if it's a double hung, the width would be given first, so I'll bet it's a 16x27....which is a really odd size for a window......you might want to check that....sounds like some kind of sales sample window.....