Energy-Efficient Windows for Old Houses

Looking to cut your energy costs and perhaps score a tax credit? Plenty of period-friendly windows and doors meet the new standards.

These triple-glazed French doors from Jeld-Wen could qualify for federal energy tax credits.

If your house still has its original windows and doors, you probably aren’t going to replace them just to earn a tax credit. No doubt you are interested in ways to cut your energy bills, though, and that means tightening up around openings.

As any member of the newly formed Interior Fenestration Council will tell you, it’s much cheaper, easier, and more energy efficient to install interior storm windows than to replace original sash. An interior storm window “gives you the same performance as a high-end replacement window,” says David Degling, owner of Innerglass Systems, and a Council member. “Our windows at $250 are as effective as a $700 or $800 replacement window. And you get to keep that original window. You’re saving history.”

Installing interior storm windows, like this one by Climate Seal, will likely reduce your heating and cooling bills by 30 to 60 percent.

It may come as a bit of a surprise that a tried-and-true preservation technology like interior storm windows are already eligible for energy tax credits, given the building market’s emphasis on replacement windows. That’s because the new standards essentially boil down to the number of layers between the inside of a window and the exterior, Degling says. Every layer of glazing, whether it’s glass or acrylic, is equal to about R 1, an indicator of the thermal value of the window.

If you’ve already got an existing single pane window, you can meet the required R value (2.84), by adding an interior storm sash plus a Lo E coating. (Lo E coatings, which turn glass into a heat mirror, weigh in at about R .9, Degling says.)

Installing any kind of interior storm window will likely reduce your heating and cooling bills by 30 to 60 percent, depending on whether the existing window is single or double glazed, says Matthew Petit, master distributor for Climate Seal. The company’s product, which is made of acrylic and seals magnetically, is undergoing thermal testing in order to qualify for the new energy credits.

For makers of replacement windows, the new standard also means they must go beyond double glazing with an air space between the two panes—the old gold standard of window efficiency that usually qualified a window for an Energy Star rating. They must also meet a slightly higher standard than the one for storm windows (the equivalent of R 3).

To meet the new standard, replacement windows usually must offer triple glazing or a combination of double glazing, Lo E film, and inert gas between the panes that adds up to R 3. Manufacturers are scrambling to create window packages that qualify.

Double glazing with Lo E film helps a window reflect the hot rays of the sun during summer. In cold weather, the reverse is true: the film—in essence, a heat mirror—reflects warm air back into the interior, while the insulated glazing helps prevent cold air from penetrating.

Jeld-Wen, which has long offered Energy Star-rated options, has come up with something called an “Energy Saver Plus” package. Windows in this category are not only double-glazed, but the inside of each pane gets a Lo E coating, and the air space between is filled with argon rather than air, says Brian Hedlund, a product marketing manager for Jeld-Wen. When configured correctly, Hedlund says, more than 90 percent of Jeld-Wen windows can be configured to qualify for the tax credits.

So how much more will these tax-credit worthy windows cost you compared to a typical double-glazed window? Jeld-Wen estimates an increase of between $1.06 and $3.05 per square foot. That may not sound like a lot, but it adds up to $50 to $65 per window for typically sized units. If your house has 30 windows, the additional cost could easily reach $1,500 —equivalent to the maximum energy credit refund. Nevertheless, if your original windows or doors are long gone, the tax credit may be just be the incentive you need to replace them with new, period-appropriate units.

While most of Jeld-Wen’s steel and fiberglass doors meet the new standards, the only wood doors that do so are its top-of-the-line custom wood doors. Although it seems counter-intuitive, glazing can actually improve a door’s energy rating, provided any glass inserts are double or triple paned. A tighter fit and improved weather stripping can boost the door’s efficiency, too. If you are loath to part with your original door, a little weatherstripping will go a long way toward tightening the seal against the elements.

For more about the federal tax credits for home improvements, visit

Tags: energy efficient heating Mary Ellen Polson OHI June/July 2009 Old-House Interiors

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