We sell Pro Type, V-shaped and Interlocking weatherstrip for double hung windows. All three types have been used effectively on double hung windows.
Of these, the interlocking weatherstrip provides the best year round solution because it allows for expansion and contraction of the window making the window easily usable.
In theory, when using interlocking weatherstrip on a double hung window the 2 sashes are locked tightly together by the sash lock at the meeting rail. The two sashes then float together on the head, sill and jamb weatherstrip. The sashes are slightly smaller than the opening to allow for expansion and contraction. The windows slide easily in the summer when the humidity causes them to swell and yet do not lose their seal when they shrink in the winter.
Saw kerfs are cut to allow the head, sill and jamb weatherstrip to fit into the sashes. Flat surfaces must be prepared inside the meeting rail to allow for the installation of the meeting rail weatherstrip. These flat surfaces may most easily be prepared using a router table.
All interlocking weatherstrip is available in both zinc and bronze. There is no functional advantage to the bronze weatherstrip over the zinc.
The author has zinc interlocking weatherstrip as original equipment on the author's 1910 house. The original weatherstrip is still intact and the wind can be howling at 50 miles per hour outside without the slightest draft.
Special Note: It is very important for all metal weatherstripping to keep paint off it. Metal weatherstrip should never be painted.