Do Covered Windows Actually Keep Homes Warmer in Winter? HVAC Experts Weigh In

Cold weather is resilient, sneaking through hidden cracks in your windows during winter and reducing the efficiency of your HVAC system. Even walking by a closed window may chill you, since glass only blocks a certain amount of heat.

To better insulate your home in winter, don't underestimate the power of window coverings. Curtains, blinds, and other treatments help keep heat in and cold out, protecting your home from winter weather and an increased energy bill.

To learn the benefits of covering your windows in winter and the best ways to do it, we consulted several HVAC pros. Here’s what they said.

Benefits of Covering Windows in Winter

Without covering your windows, you will undoubtedly notice a difference in your home during the winter months. "Cold surfaces in your room, including windows, pull radiant heat away from you because heat always moves toward colder objects," says HVAC and air quality expert Glenn Gault. "This is [why] you feel chilly even without touching the window." The following is a list of benefits for keeping your windows covered in the wintertime.

Keeps the Heat Inside Your Home 

Windows are the weakest point in most houses when it comes to heat loss, says Matt Gorbacz, HVAC expert and owner of Clean Air Technologies. "Even good windows can let heat escape," he adds. Any type of covering, whether it be curtains, blinds, or thermal panels, will create an extra insulation layer that traps heat. "This will also take some pressure off the heating system and keep rooms warm for longer," he says.

Minimizes Drafts and Cold Spots

Many homes have invisible gaps around windows. This is where the cold sneaks in. "If your home has drafts around old windows, covering them will reduce the outside air coming in," says Gorbacz. "This is one of the easiest ways to fix cold spots in bedrooms and living rooms without major repairs." 

Remember that certain leaks may be so small that you don't notice or hear the draft. "Tiny gaps in weatherstripping and micro-gaps around the sash never 'whistle' but let cold air in and increase your heating bills," adds Gault.

Lowers Heating Costs

Because covered windows improve heat retention, your furnace or heat pump doesn’t have to work as hard, lowering your heating bill in the process, says HVAC expert Tamer Sayed. You are likely to see a drop in your winter bills simply by insulating your windows properly, he says. 

"Covering windows with thermal or just thick curtains significantly reduces heating bills in winter — up to 20 percent in homes with old and drafty windows and up to 10 percent in homes with new and good quality windows," says Gault.

Reduces Condensation and Moisture Buildup

Cold glass attracts a lot of moisture, which can lead to mold around the window frame, says Gorbacz. Covering your windows properly helps maintain a more stable indoor temperature, minimizing condensation buildup on windows. Doing so will protect your trim, paint, and even nearby drywall from mold growth and moisture damage.

While curtains will not entirely stop condensation from forming on the glass, they will reduce the amount of warm air that reaches the cold window surface, resulting in less moisture buildup, notes Gault.

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The Best Ways to Cover Windows in Winter

If your windows are letting cold air into your home, chances are your treatments are lacking. To help, we're sharing the most effective ways to protect your windows in winter. One may suit your house and personal tastes over another, so it’s good to become familiar with your options.

Thermal or Insulated Curtains

Thermal curtains are one of the most effective and good-looking options. "They block drafts, stop radiant cold, and trap a warm air pocket between the curtain and the window," Gault says. Hang them so they fully overlap the window frame on all sides and close them at night or when temperatures drop, Gorbacz adds. On sunny days, it is recommended to leave your curtains open to let in the natural heat.

Cellular or Honeycomb Shades

Cellular or honeycomb shades present an entirely different aesthetic, which may be better suited to your interior style, type of windows, or personal taste. Not only do they beautifully diffuse natural light (or offer total blackout), but they also reduce noise levels while keeping the heat from escaping.

"These shades have air pockets that act like insulation," says Gorbacz. "They reduce heat loss through the glass by creating a sealed layer." He recommends mounting them inside the window frame and lowering them completely at night for best results.

Custom-Made Window Frames With Plastic

If having an open view of the outdoors is important to you, custom-made window frames with plastic may be your best bet. While a professional can help with installation, for those with a DIY mindset, Sayed recommends cutting wood strips to the size of your window frame. Make sure it fits snugly on your actual windows. Then attach plastic film on both sides of the frame. The frames can be removed once it warms up.

Window Plastic Film Kits

Another way to keep your view unencumbered while insulating your windows is to use window plastic film kits. "Window insulation film is effective even on single-pane windows because it creates a sealed air barrier that prevents warm indoor air from touching the cold glass and dramatically reduces heat loss," adds Gault. It is a low-budget option that will stop the drafts and reduce heat transfer through the glass.

To use the kit, he says to start by cleaning the window frame. Next, put double-sided tape around the perimeter of the window frame. Unroll the plastic film and press it onto the tape. Using a hair dryer, shrink the plastic to secure it tightly. "Applying it too loosely will cause the kit to lose its effect," says Sayed.

Bubble Wrap

In a pinch, you can use bubble wrap to add an additional layer of insulation to your windows during winter. "Measure your window panes, then cut the bubble wrap based on the panes' sizes," says Sayed. To cover windows with bubble wrap, spray the glass with a light mist of water, then place the bubble wrap securely on the glass with the bubble wrap facing the window. 

Winter Window Mistakes

Even with proper window coverings, there are some common mistakes homeowners make when protecting their windows from winter weather. These are the pitfalls our experts warn against.

• Keeping curtains closed during the day: "Sun provides free heat, and it’s a big mistake to block it during daylight hours," says Gault. Similarly, closing your curtains at night will keep the heat in.
• Leaving windows bare in winter: "Glass loses heat fast, and not adding even a basic covering can make your space colder and raise heating costs," says Gorbacz.
• Covering radiators with curtains: If you have radiators under your windows, avoid covering them with curtains. "Radiators need a free path to heat the room," notes Gault.
• Not fixing rotting or peeling window frames: Fix any deteriorating window frames before the cold weather sets in to keep your home warm and avoid putting stress on your HVAC system.
• Using single-pane windows: Single-pane windows have almost no insulation value. "Even if the frame is perfectly sealed, the glass itself is still too thin," says Gault. Double-panes and triple-panes will increase insulation, reduce noise, and lower your energy bill.
• Using curtains that are too short or narrow: "If the curtains don’t fully cover the frame, heat will escape around the edges," says Gorbacz.
• Not sealing drafts before adding coverings: "Coverings alone can't fix air leaks," cautions Gorbacz. Check for gaps around the frames and add weatherstripping first.