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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. By Gordon Bock

    Many companies offer new windows that take cues from historic architecture. Kolbe has Classic and Heritage window series.

    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 Marvin.

    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 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.

    Published in: Old-House Interiors July/August 2011


    Tanya May 19, 2011 at 3:31 pm

    Don’t forget that you can increase the performance of your old windows by having a storm window made for the winter (here in the North) or summer (South?). Plans and directions can be found online or by visiting forums such as the one for Old House Journal. I’ve been told that they can make your current windows give those new and improved replacements a run for their money. :)

    Nancy S. May 19, 2011 at 4:25 pm

    Anyone know of energy efficient windows to replace 1950 metal-framed lever opening windows, multi-light spanning 6 feet?

    Mike J May 22, 2011 at 8:19 am

    The use of storm windows, including a new generation of high performance storm windows with low-E or insulated glass, is one of the most cost effective and energy efficient strategies. Because storm windows haven’t been receiving the massive advertising attention that has been given to replacement windows the public is not well informed on this great benefits of historic retrofit approach.

    Brian C January 4, 2012 at 11:20 pm

    I agree with keeping your old windows and adding storm windows. It makes so much sense in so many ways. One that is not often mentioned is that the quality has much improved and they can be ordered in dark colors, which old house sashes were often painted for the windows to recede. They just look better darker and especially stand out from all the other white plastic windows. My windows are 109 years old and will still be there at least until I’m gone. Once they’re gone they are gone. Think twice don’t replace once….you’ll probably have to replace them again and regret it many times.

    Catherine Brooks February 15, 2013 at 2:03 pm

    Yahoo for the author pushing to repair not replace centuries old windows! Even if the wood parts have rotten spots, they, too, can be cleaned and filled with epoxy. But strip the old, lead-based paint totally off and remove the glazing first. Infrared paint remover, Speedheater (, can do both safely and minimize the risk of broken glass and wood damage. Once the glass is reseated with new glazing, the ropes or metal pulleys replaced, and the sashes and frames beautifully repainted, weatherizing is a must. As mentioned by the author, there are many options of new storm windows which can be mounted on interior or exterior and not obstruct the historic beauty of the restored window.

    Philip Riutcel May 14, 2013 at 10:09 am

    There has been an updated study out of UCSB (University California Santa Barbara) that shows that dual glazed windows are not so green after all. Inferior material that needs to be replaced far more often, along with leaking vapor/gas barriers, makes most new windows green for the in money not the environment. Vinyl clad windows do not hold up to UV exposure, and the LVL laminated rails and styles so popular now decompose when water penetrates the 1/32″ veneer. On the other hand there are windows that are well over a hundred years old that work perfectly, and will continue to do so if maintained (sanded and repainted or stained)…the secret? Solid stock, quality material. Do the math replace every ten years..or less, and fill up a landfill, use ten times the energy, as well as fossil fuel glues ,solvents, and cladding or build once and have a lifetime product. Of coarse China does not care how long their products last….Big picture here folks…Look at the big picture.

    Steve December 6, 2013 at 5:40 pm

    I had a neighbor replace classic leaded casement windows in a beautiful tudor home with plastic looks awful. And whats worse is they have no idea what they have done!

    Sheridan December 19, 2015 at 3:23 pm

    We have found that good heavy curtains can make a huge difference! And they are the most economical choice since if necessary you can make them yourself. We are working on the preservation of an 1860 brick farmhouse with Italianate details. The windows are made out of wonderful old growth wood – and have survived beautifully despite at times decades of neglect, since they were made with the care we now only assign to fine furniture.

    The curtains need to have a good interlining as well as the regular lining. They need to completely cover the window and trim, and be opened and closed as appropriate for blocking either cold or hot weather. Easy as that. Of course we also working on weather stripping (tip- if you need to do something quickly we
    have found white or clear painter’s tape over gaps works great).

    Charles from Sudbury Insurance July 12, 2016 at 5:51 pm

    I wonder what the difference in value between having antique/old-style windows vs. energy-efficient windows. One increases your home value via aesthetic appeal, the other saves you (and the next homeowner) money each year. Do you know if insurance rates change based on energy efficiency?

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