if you wish to retain existing wood sash window frames,even if they may be frozen/painted shut,with small hand tools,other improvised doo dads,plus nu putty, to reglaze them,many of these old timers can be made young again,unlike the old timer who trained me,,and will last another 30-50 years,clean & polish the glass with warm h20 & pumice,bed the glass in a thin film of nu putty,(treat wood with boiled linseed oil),a 16th in thick,point the glass in,apply a bead of warmed putty, use a 3q in bent/curved flat knife to smooth the angle.nu putty forms a thin skin in a couple weeks,the bead will still be weatherizing,soft underneath after 40 years.excellent stuff. bustem glazing we never breakem