Q – My old windows are not worn enough to replace, but they are drafty, sweat during cold spells, and the furniture fades. I saw some low-cost, reusable interior storm window kits. Are they worthwhile?-Karl H.
A – Reusable rigid interior storm window kits are an excellent low-cost, energy-efficient alternative to replacement windows if your present windows are still in reasonably good condition. Many are designed for simple do-it-yourself installation and others can be dealer-installed. With proper care, these storms will still look like new after 10 years or more.
In addition to windows, don’t forget any skylights that you have. Skylights, particularly older ones, can lose a substantial amount of heat and cause fading of furniture and carpeting. I installed a magnetic storm window kit in my own living room under a new super-efficient double-pane skylight.
Unless you use natural ventilation in the summer, leave the interior storm window kits up year-round for the most savings, outdoor noise reduction, and comfort. With the narrow plastic frames, the storm windows are barely noticeable. The frames are available in several colors or you can paint them to match your walls. If you have natural wood window frames, select a kit with wood-grained frames.
Most storm window kits use lightweight clear acrylic because it insulates better than glass and is safe and easy to work with. For the lowest cost, you can often mail-order the frame kit for your window or skylight and then buy standard acrylic sheets at any local home center store.
Acrylic is a crystal-clear plastic and yellows over time like other plastics. It is very impact-resistant (safe around children) and naturally blocks nearly all the sun’s fading ultraviolet (UV) rays. For the greatest strength, choose polycarbonate (“bulletproof glass”) plastic. It is more expensive and will yellow slightly over time.
If you have a window condensation problem in the winter, interior storm window kits can help. You must first paint the inside surfaces of the window opening with a sealer type of paint, then paint it with your regular wall paint if you like. This blocks indoor moisture from passing through the drywall and getting between the storm and primary windows.
There are many designs of interior storm windows. Ones that use quick-to-install magnetic seals are the most common. To make them less noticeable, they can be mounted directly against the primary window frame (creating a small dead air space) or inside the window opening on an L-channel.
Another option is to mount them over the entire window opening, overlapping on to the wall by an inch or so. This is the easiest installation method, but the deep air space between the storm and the primary windows will allow wasteful air currents to develop between them.
A magnetic strip, usually about half an inch wide, is embedded in the rigid vinyl storm window frame. A thin, self-adhesive steel strip is attached to the wall or window frame. The powerful magnet holds the storm window snugly against the strip for an airtight seal.
Other attachment options are clips and hook-and-loop strips. Clips are often used on very large storm windows and are easy to install and remove each year.
For very drafty old windows, select a kit with a secondary seal in addition to the primary attachment seal. If you have slider or double-hung windows, select a split kit that allows half of the window to be opened.