Storm windows are a boon to saving energy and keeping your home comfortable. they also can serve as a protective barrier against wind-driven debris during storms. Whether you put them up each season or use versatile double or triple track storm windows, they effectively add insulation to your home. Old single pane windows have an "R-value" of about one. Adding storm windows effectively doubles that. While an additional R-1 might not seem like a big deal, it doubles what you already have. Imagine how cold your home would get if you left those windows wide open. So R-1 is worth the effort.
If you don't already have storm windows, you can order windows through a variety of sources, including home improvement centers. Interior storm windows can be easier to install, especially upstairs, but they can detract because of their appearance. Interior storm windows may be your only choice if your community has rules that do not allow exterior storm windows. Exterior storm windows tend to be more durable and more effective. Double track windows have two tracks, one for a sliding window, the second track for the other window sash and the window screen. In this unit, only one window sash can be opened, but that operable window means they can be left up year round. Triple track models are even better because each window sash can be opened; each gets its own track with the third track being used for the window screen. If you don't want to make the investment in permanent storm windows right now, you can use heat-shrink film to create effective temporary storm windows.
The key to storm windows is that they fit snuggly into the window opening. If they don't fit well, drafts will reduce their insulating effectiveness. Some people apply an adhesive caulk around the storm window to get the best seal. However, the bottom should NOT be caulked. If you caulk the bottom, any water that finds its way in, along with condensation will be trapped inside the unit. The pooled water can cause all sorts of problems and damage.