I’ve lived in my condominium for several years, and though it naturally stays cooler in the summer (with all west-facing windows) I struggle to keep it warm in the winter without taking out a loan to pay utilities. Like any homeowner, I must answer the question: Is it better to try and insulate my existing window, or am I better off replacing it? Sometimes the answer is purely about upfront costs, but other times the inefficiency more than justifies the cost of replacement.

There are several ways to make windows more efficient: The least expensive method is a simple window insulation kit, which includes a large sheet of plastic and double-sided tape; the most expensive (and most efficient) method is to replace the window with an energy efficient, double-paned window, which traps incoming air between the two panes and stops drafts (of course, if you’re going to buy a window you may as well take advantage of any available tax credits).

This season I used a window insulation kit to stop the drafts in my bedroom window. In past years, the insulation has been enough to keep cold drafts out, but this year is different. On windy days, I can actually see the plastic bulging and wonder if it will come loose. It hasn’t yet, but I have seen a new threat: Condensation is building on the plastic facing the window. This is bad – not only does it indicate that my window is WAY overdue for replacement, but it also can lead to mold buildup. Mold is dangerous both to the building and to the air we breathe.

So now that I’ve seen these horrors on my window, I am faced with the need to replace it. I’m keeping an eye out for a sale on the type of window my HOA requires (though I may not be able to wait that long), and looking forward to a cozier bedroom.

Andrea Spikes is a communicator at DOE's National Renewable Energy Laboratory, which assists EERE in providing technical content for many of its Web sites.