Generally speaking, while maintaining their historic look in energy efficiency a reasonable upgrade can be achieved by restoring old windows. However, you must ensure that the voids around the window are caulked and insulated properly. Also, to increasing the energy efficiency whether exterior or even interior a properly fitted storm window will go a long way. Doing this kind of work there are specialists.
If your house windows on the world no longer enhance the facade of your house, filter out noise or shield it from the elements, with new ones that will complement your home's architecture it may be time to replace them, increase your comfort, reduce your energy bills, and promote quiet and peace.
There are certain attributes you should consider if you do want to go the way of low-U window a new double-pane, and low-E.
Replacement windows are of two types. Without undoing and redoing the sill and trim within the existing opening a window that fits is termed as Window replacement in the industry. Usually fitting into the existing opening this type of window though small will have an additional frame. The thickness of the window frame is increased and the net amount of glass can be reduced by this. By window manufacturer this thickness varies, and with what your condo association or you would want it may not be aesthetically compatible.
Otherwise, with a “new construction” window you can replace your old window. Frame-within-a-frame look is not present in this. In the existing location of your window it can be installed, but this would mean installing the new window, taking out the existing casings and frame, and doing painting and patching and reinstalling all the trim.
While giving you the energy efficiency you are looking for, this would look the best but as compared to a replacement window to install it would cost more.
In either case, the small wood pieces that hold each piece of glass in place is called muntins assuming that there are individual panes and your windows have a grid. You should look at the muntin width and profile when deciding on whether to replace windows and doors.
May or may not match your muntin, each manufacturer has a standard profile. Around ¾ of an inch wide older windows generally have narrower ones. As their narrowest some new window manufacturers have only 7/8 of an inch.
To retain a historic look the exact profile of the muntin may be important. Old windows typically have curved “ogee”-style muntins and relatively flat or plain some window companies have muntins. An S-shaped profile means Ogee. When considering which way to go try to find one that matches as closely as possible.
When choosing a new window another feature to examine is how the edge of the window is met by the muntins. Do they look a bit blunt is it in a graceful and tapered way?
Finally, ensure to know the materials utilized. While some type of protective layer, called cladding on the outside is good Wood is nice on the inside. Such as vinyl or aluminum each window manufacturer has its preferred cladding material.