Install DIY storm windows to reduce drafts
Q: I have double-pane windows, but I think it would still help to add some storm windows. I am planning to make them myself. Are interior or exterior storm windows best? How can I design and build them?
A: Since you already have double-pane windows, do-it-yourself storm windows are the most cost-effective option. The much higher cost of professionally installed storm windows would likely take a long time to pay back with energy savings.
Storm windows save energy by creating a dead air space and by reducing air leakage. Although it is counterintuitive, a narrower air gap between the window glass and the storm is better.
If the air gap is more than 1 inch wide, circular air currents can develop within the air gap and soon it is no longer a dead air space. When this happens, the insulation value of the air in the gap becomes ineffective. The only insulation value increase is from the plastic sheet or film, neither of which is very high.
In general, exterior storm windows that cover the entire window opening provide the greatest efficiency improvement. Even though the air gap may be wider than optimal, they reduce convection losses from the direct force of cold winter winds and reduce air leakage around and through the window.
The drawback to exterior storms is they must be built much stronger to resist the outdoor weather. Making interior storms is much easier and there are do-it-yourself kits available to help make them.
Using polyolefin shrink film from a storm window kit, but making your own wooden frame, works well. It can be removed each summer and reused for years. This looks much better than just sticking the tape on the window frame.
Make the rectangular storm frame about one-quarter inch smaller (room for weatherstripping) than the inside dimensions of the window opening. Paint both sides of the wood frame, because the tape sticks better to a painted surface. Cut a piece of the shrink film and stick it to the tape.
Place another strip of tape over the film. Make narrow wood strips and staple them to the back side of the frame over this second strip of tape. This holds the shrink film much tighter when you shrink it with a blow dryer. With just a single piece of tape, the film may come loose and allow air leakage.
Red Devil has recently developed an interior storm window kit called Snap N Seal. It uses an adhesive-backed plastic frame material that sticks to the window frame. Cut the frame pieces to fit the window. Cut a sheet of clear acrylic (which also blocks fading rays) to fit. The indoor edge of the frame snaps open and closed so the acrylic sheet can be removed in summer.
Another option, Indow Window, is a frameless acrylic storm window sheet with molded silicone weatherstripping around the edge. It is made to the exact size of the interior window opening. It is just pushed into the window opening close to the glass to create a small air gap each winter.
This story was originally published January 22, 2015 at 9:55 AM with the headline "Install DIY storm windows to reduce drafts."