8 Tips for Energy-Efficient Old Windows

Repair or replace? The ongoing tug-of-war has gotten more heated with renewed concern about energy use. Here are 8 guidelines to help you decide.
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Repair or replace? The ongoing tug-of-war has gotten more heated with renewed concern about energy use. Here are 8 guidelines to help you decide.
Many companies offer new windows that take cues from historic architecture.  Kolbe has Classic and Heritage window series.

Many companies offer new windows that take cues from historic architecture.

It’s hard to imagine any other architectural feature as debated as windows. They’ve been called the eyes and even the soul of a house, so the aesthetic and historical concerns with replacement windows are justified. Then again, windows represent high maintenance and also heat loss, so practicality weighs in. The recent emphasis on “green buildings” has heightened the decades-long debate.

Whether you’re inclined to cherish them or chuck them, windows deserve consideration with a new urgency in the 2010s as the federal government dangles tax credits for home energy-efficiency improvements, and as manufacturers extol the virtues of their new thermal performance standards. What’s an old-house lover to do?

There’s no litmus test to tell us whether replacement windows are good or bad. The goals for each house and each project are different. Numbers do not tell the whole story. What we can do, however, is organize our thinking to cut through confusion and see the subject in a clearer light.

1. Understand that the window change game is nothing new.

This attractive 12/1 sash is from Marvin.

This attractive 12/1 sash is from

If you think the bombardment of print and TV ads telling homeowners to upgrade old windows is a new effort, think again. The transformational possibilities of replacement windows have been preached since at least 1865, when architect George Woodward, author of Country Homes, showed “How to Re-Model an Old Farm House” by adding a dormer window in the roof and a bay window to the main room. By the 1920s, it was the manufacturers who pitched new windows as a way to modernize: “…it’s changing the drab and ugly to the cheerful and beautiful.” During and ever since the back-to-back oil crises of the 1970s, an energy spin was added to the allure of window makeovers.

2. Appreciate the value of historic windows.

When an old house is in a historic district or otherwise subject to architectural review, potential changes to existing windows put authorities (like a historical committee) on high alert. The reason, according to the Secretary of the Interior’s Standards for Rehabilitation (the accepted benchmark for evaluating proposed changes to historic properties), is that the old windows are “an important aspect of the character” of a building, and changes should respect “the significance of original materials and features…repairing and retaining them wherever possible.”

Aesthetics aside, every year, the dollar case for historic windows quietly grows a bit bigger. In real-estate markets where vintage architecture is part of the appeal, there’s evidence that sensitively maintained old houses hold their value. Certainly, insensitive changes to windows can translate to lost dollars when it derails paperwork, such as for a historic tax incentive (which, in some states, can still represent as much as 20 percent of the dollars spent on rehabilitation). From a go-easy-on-the-planet perspective, sending a set of windows to a landfill wastes all the energy used to make them, even as energy is expended making their replacements.

Pella manufactures historical casement and divided-light sash windows.

Pella manufactures historical casement and divided-light sash windows.

3. Get an energy audit.

The first step in any kind of problem-solving (in this case, how to use less energy) is to define and limit the problem. An energy audit is an excellent way to define where energy loss is occurring, be that heat loss or heat infiltration (a problem in summer). An inspector surveys the building using tools such as thermal imaging cameras. In an infrared photo, blue indicates cold spots: leaks you may not even feel or be able to see with other methods. Conversely, areas that run yellow to orange and red indicate warm spots, including heat loss viewed from the exterior. Tools include blower doors that measure the extent of leaks in the building envelope, particularly through windows and doors. An audit might cost $250 to $450; some utilities do free auditing for issues related to their services.

4. Deal with drafts.

Infiltration of air from the outdoors is in fact the major contributor to heat loss at windows—not conduction through the glass itself. If infiltration pathways are not addressed, the problem may remain even if the sash is replaced. Dealing with drafts, not springing for thermal-pane windows, is perhaps the most cost-effective thing you can do to improve efficiency and comfort. And these fixes are usually low-tech, even do-it-yourself. Start by looking for telltale drafts with a smoke source (us post-Woodstock types use incense sticks rather than cigarettes) or a smoke pencil puffer stick, a home inspector’s draft detector that creates plumes of non-toxic “smoke.”

Start with the usual suspects: at the meeting rails (the juncture of top and bottom sash in the middle of the window), stop moldings (vertical strips at either side of the sash), sash-cord pulleys, and outside trim. Simply fine-tuning the stop moldings and using your sash locks (which pull the meeting rails together) will often greatly reduce leakage. Retrofitting the sash with weatherstrips may cut drafts even more. Pulleys can be exchanged for insulated types that seal where the rope exits, or tape balances that eliminate the cord and weight in lieu of a clockwork spring. Also caulk the exterior trim.


Do you need more tips on fixing windows? Learn more about sash window repair.

Parrett Windows manufactures custom-crafted windows for historic preservation projects.

Parrett Windows manufactures custom-crafted windows for historic preservation projects.

5. Realize the attic may get you the most bang for your buck.

If your concern is conserving heat, remember that most of the heat loss in old houses is not through doors and windows (which studies peg at 12 to 25 percent), but through the roof (which can be as high as 30 to 40 percent, depending upon the building’s condition). The point is, adding or increasing attic insulation may be the best first place to spend your energy improvement dollars.

6. Put pencil to payback.

Going by numbers alone, such as the U-value rating (the rate of heat loss), the best new windows do look much more energy efficient than older windows, even modern windows just 20 years old. But the payback may be longer than you think. To save money, a new window has to first recoup its upfront costs (say, $400 installed for a standard 36" x 60" unit) in energy saved—that is, a reduction in the energy bill. If the new, double-pane thermal window has a U-value of 0.58, versus the U-value of 1.10 for the existing single-pane window (that’s without a storm window), it might save 625,922 Btu a year. At $0.95 per therm, this would mean an energy savings of $9.65 a year. At that rate, it would take nearly 40 years to just pay for the window, even with the 2011 energy tax credit of 10 percent. What’s more, for even the most optimistic payback, the new window has to maintain its out-of-the-box performance until the break-even date. This is by no means a sure thing, given that most thermal windows have shown a tendency to leak insulating gas and otherwise break down over time.

Architectural windows are more widely available, including round-top sash and divided-light transoms like these from Pella.

Architectural windows are more widely available now, including these divided-light transoms from Pella.

7. Consider heat gain in the equation.

It’s not only heat loss that is the problem, but also heat gain—the primary concern south of the snowbelt, where it wastes energy dollars by making air conditioners work harder. Heat gain results when the long-wave radiation component of daylight passes through a window. The best new windows address this by incorporating various low-e (low-emissivity) technologies, such as special coatings on the glass or films between double panes. Such technologies are typically not part of the construction of older windows. (In some cases, historic sash or storm windows have been retrofitted with low-e glass.)

8. If you choose replacement windows, keep them in kind.

Match the architecture. When shopping for new windows (not only as replacements, but also for remodeling and additions), choose units that come closest to the character of your historic windows and your old house. Without custom fabrication, you may not be able to exactly duplicate dimensions, but you should be able to come very close to the original proportions and design.

For sources, see the Products & Services Directory.