How Windows Can Improve Home Energy Usage

by Rachel Lyon, Editorial Director for Direct from the Designers™

As cooler temperatures set in, you might notice a chilling draft by your windows. That harbinger of winter is just the beginning of months of high utility costs, but it doesn’t have to be that way. When you invest in quality windows, you can slash heat loss and facilitate passive solar heat gain, so they are a major asset of energy-efficient design. Here’s how to select the best windows for your needs!

Marvin Ultimate Casement

A gorgeous window design featuring large Marvin Ultimate Casement Windows gives this room a broad view of its surroundings. See more of this low maintenance, highly sustainable home in the Lyme Guesthouse Case Study.

The Most Inherently Efficient Window Types

Before getting into the technical specifics that affect window performance, there are some kinds that are more efficient based on construction alone. Window seals are potential weak points, so consider how windows open. Hinged windows—like casement and awning—have weatherstripping that presses to a seal between the window and its frame when locked closed, but sliding windows—like double hung and side-to-side gliders—are made of sashes that pass beside one another within the frame, and they require flexible seals as a result. You can understand how structure produces an efficiency difference between a window that creates its own compression seals and one that must have seals flexible enough to allow movement.

When you think about the history of windows and house styles, you’ll find that as glass manufacturing improved, modern architecture took off. And if you know anything about modern homes, they are defined by their ample use of windows. If you’re going to choose a home with that much glass, it had better be efficient! That’s one reason why hinged windows are typically chosen for these applications, while single and double hung window styles are primarily used for their historically accurate looks on older, traditional architecture. Remember that windows weren’t nearly as large in the past, and if you love the classic appearance but also want the broader expanses of glass that we prefer now, you should weigh the pros and cons from an efficiency and stylistic standpoint. For the sake of their utility costs, many people have opted for casement windows with divided lites to get the best of both worlds, but advanced engineering means that high quality sliding windows are also efficient these days.

Integrity Wood-Ultrex Casement Windows

This stunning lake view home includes Integrity® Wood-Ultrex Casement and Awning Windows as well as Inswing French Doors. Ultrex® is a super durable fiberglass product—read all about it and see it put to the test here.

Durable Materials with Low Thermal Conductivity

A lot of the time, that draftiness you feel isn’t actually an indicator of air movement. If the pane of glass or its frame is thermally conductive, the high radiation rate is why you feel the temperature transfer. Explore options to minimize this rate and maximize efficiency.

Frame material can make or break window efficiency. Aluminum is often chosen because it is lightweight and practically maintenance-free, but you know exactly how cold metal gets in the winter. You’d much rather handle wood in low temperatures, but wood frames require regular upkeep to prevent degradation from the elements. Put these two together and you can make a fantastic window that is less thermally conductive than metal and more durable than wood. If you want aluminum clad windows, be sure to select extruded over roll form aluminum, because it is much thicker and stronger. While that protects the exterior, you can enjoy the beauty and warmth of wood from the inside.

Vinyl is popular because it resists moisture, but it is brittle in the cold and can warp in strong direct sunlight. It also expands and contracts at a rate seven times greater than glass, meaning that seasonal temperature swings can break insulating seals around the panes. Fiberglass is the best insulator among window frame materials; it shrinks and expands at virtually the same rate as glass, which makes its seals as durable as the rest of the unit. While fiberglass has a higher price tag upfront, it will save over time thanks to its durability and efficiency.

As far as glass goes, double panes with insulating gas have become standard. The gap between the panes creates a temperature buffer on its own, but adding gases like argon and krypton further decreases heat transfer. Tripane windows are available for the super energy conscious consumer, but they do come at a higher cost. Whether it’s double or triple paned, the glass itself isn’t often the problem, and that’s why efficiency usually comes down to the quality of the frame. You need to compare U-factors—which measure the heat transmittance of the entire window unit—to determine the efficiency, but they don’t account for frame durability. The lower the U-factor, the smaller the heat transfer and the greater the efficiency, but that doesn’t mean much if the frame rots, warps, or expands and contracts to break the seals in a few years. It’s up to you to look beyond the U-factor to determine which windows will remain efficient for the long term.

Integrity Wood-Ultrex Sliding French Doors

Integrity® Wood-Ultrex Sliding French Doors are a beautiful addition to take in views and have glazing options just like windows. If you live in a southern location, you should also consider a shade-creating overhang to help keep the heat out, like these homeowners did.

Maximizing Efficiency with the Right Glazing

While everybody can appreciate windows that are durable and provide a good level of insulative power, there is no "one size fits all" solution. In addition to multiple panes with insulating gases and a range of frame materials, modern technology has added another variable: glazing. You can’t see the microscopically thin metallic glaze applied to the glass, but it plays a crucial role in controlling the exchange between indoor and outdoor environments and contributes to both the U-factor and the Solar Heat Gain Coefficient (SHGC). Low emissivity (Low E) coatings are selected based on climate zones to optimize windows for their surrounding conditions. Low E1, for instance, contributes a low U-factor and has a high SHGC; it reflects indoor heat back to prevent loss to the outdoors and allows the sun’s heat inside, so it is best for cold northern climates. Low E3, on the other hand, contributes to a low U-factor and has a low SHGC, meaning it insulates well and reflects the sun’s warmth away, making it ideal for hot southern areas. If you don’t know which glaze is best for your needs, you should consult with a professional who will take location and home orientation into account.

So, if glazing affects heat flow, can it overcome the window’s reputation for being the weakest link in the building envelope? If you play your cards right, absolutely! While insulation in exterior walls slows heat transfer in both directions indiscriminately, glazing directs heat where it’s wanted to improve the whole home’s efficiency. So, if you want large windows to take in views or lots of natural light in a northern location that gets very cold, opt for a Low E1 coating and point the majority of your windows due south. That way, you get light and the extra boost of free solar heating. In southern climates where reducing cooling costs in the major concern, Low E3 glass is perfect. When you invest in quality materials that can withstand the conditions and help you overcome them, your home can rely less on the HVAC system and save money for many years.

If you’re ready to make that investment, check out the wide variety of windows and doors from Marvin® and Integrity®. With plenty of shapes, styles, and finishes to explore, you can get lost in the design possibilities without worrying about utility, because these brands are committed to energy efficiency and can help you select the best products for your needs. Find a local representative who will get you on the way to a more environmentally friendly home!

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