Q: Our house has original single-pane windows, and we always feel chilly near them. I got quotes on having them replaced, but I can’t afford it now. What can I do in the meantime to improve the efficiency of the old windows?
A: I am not surprised you feel chilly near old single-pane windows on a cold day. They typically have huge heat loss and cold-air gain because of poor caulking and weatherstripping (if there is any to begin with).
The most significant heat loss and chilly feeling occurs on a clear winter night. The R-value—a higher-the-better number that shows the ability of insulation to resist the transfer of heat—of a single pane of glass is only R-1, compared with an insulated wall at R-20.
You can do many things on a limited budget to improve the year-round efficiency of your windows. Before you make any improvements, check the caulking and weatherstripping on the windows and ensure the framing is not deteriorated. If you find subpar conditions, fix them before you make improvements or your hard work won’t be worth much.
Adding storm windows, interior or exterior, can more than double the energy efficiency of your windows. Custom-made, multi-track storm windows often cost almost as much as new windows, so make your own using clear acrylic sheets. An advantage of using acrylic instead of glass is that acrylic blocks most of the sun’s fading ultraviolet rays.
Exterior storm windows can be made with 1-by-2-inch lumber, acrylic sheet, and foam weatherstripping. If you size them to fit inside the wall opening and paint them to match your existing window frames, they will look like part of your windows. The compressible foam weatherstripping should hold them in place in the opening. Push them in as far as possible to minimize the air gap.
To install interior storm windows, use a kit with magnetic seals. The magnetic section of the seal attaches to the acrylic sheet with an adhesive backing, and the steel strip attaches to the window frame. This allows you to easily remove them during summer for ventilation. If you use air conditioning most of the summer, just leave them up year-round.
Another option is to install insulating window shades or curtains to increase the overall insulation level of the window opening and to block the radiant heat loss from your skin through the window.
Some of the most efficient window shades can add R-6 insulation to your windows. These are multilayer roll-up shades with a heat-reflecting airproof inner film layer to greatly reduce radiant heat loss or gain during summer. These shades are particularly effective because the side edges slide in channel tracks, which reduces the amount of air that circulates against the cold glass.
The newest energy-saving permanent window films are also effective for reducing wintertime heat loss. They have a slight tint so they can’t be detected and use the same type of microscopically thin low-emissivity metallic coating as expensive replacement windows. Simple vinyl static-cling film will also help. But before installing anything on double-pane windows, check the window manufacturer’s warranty regarding film application.
Do-it-yourself energy-saving film installation kits are available at most home improvement stores. Depending on your climate, you may want to select a darker tint if summertime heat gain is your most significant concern. Because the sun is higher in the sky during summer, installing window awnings for shade and a lighter film on south-facing windows will allow for some passive solar heating from the lower wintertime sun.
A final option is to install a tilt-in double-pane, sash-only replacement kit. If your existing frames are in good condition, this will convert your old windows into very efficient ones. This option also provides the convenience of tilt-in sashes for the ease of cleaning both sides of the window glass from indoors.