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How to Insulate Old Windows: Three Budget Approaches

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When it comes to insulating old windows against cold winter air or scorching summer heat, there are few options that serve as much more than “band-aids.” That said, if replacement windows aren’t in the budget, here are three ways you can better insulate windows. Many of the same methods can be used to insulate glass doors as well.

Determining whether or not your windows are good enough to keep you comfortable and shielded against outlandish energy bills used to be as simple as holding a candle near glass to see if it reveals two reflections (indicating that they’re double pane). These days, however, the Environmental Protection Agency includes some double-pane windows among those that contribute to billions of dollars in energy losses each year—many of which might not be as old and outdated as you think. In other words, even some double-pane windows are in dire need of updating. Those estimates are partly based on the U-factor ratings of windows and insulating glass, which is the measurement for how well they prevent transfer of heat, thereby keeping it in your home. Appropriate U-factor ratings vary by climate and region, but it’s suffice to say that in most areas a rating of 0.50 (the lower the number the better the performance) isn’t going to do a very impressive job of keeping your heat in, translating to the chill you feel in winter. As late as the 1990s and early 2000s, 0.50 was pretty typical. These days, even the least expensive doors and windows clock in at nearly twice as good.


Identifying antiquated windows is no longer as simple as spotting single pane (versus double- or triple-pane) insulating glass.


For those windows that are stuck in the past, measures such as plastic films, foam seals, caulking and even those little cloth, homemade “snakes” you see at grandmas—they all help a little, but most do nothing to improve U-factor. For this reason, there’s no patchwork of solutions that serves as a viable alternative for replacement windows, but they can help if you’re in a pinch. In order to decide which is best for your home, first you’ll need to do a little analysis.


Step 1: Pinpointing Problems with Your Insulated Windows

There are three ways for heat to escape through doors and windows. The first and most damaging is simple: by air leakage. Experts agree that an opening even as thick as a credit card will do immense damage by allowing warm air to leak out and/or cold air to leak in, diluting your home’s temperature and comfort. Other methods include by direct transfer through door and window components and glass, via conduction and convection.

Conduction occurs when the heat energy in your home’s air collides with the surface of glass or window components, raising their temperature. That heat is then conducted through solid materials where it meets the outside air and escapes. The conduction process can be inhibited by insulating materials, such as insulating glass or expanding foams, as well as air chambers (gaps) that serve as thermal breaks. You’ll find those touted as features in new replacement doors and windows. But in cases where air chambers are large enough, convection also occurs, when heat energy radiates off of one surface before cycling through the air to another. In this way, convection is the process by which heat energy “leaps” from one side of a door or window to another in order to escape via conduction.

Most double- or triple-pane insulating units incorporate one or more air spaces between layers of glass and fill them with specialized gases, such as krypton or argon. This cuts down on both convection and conduction. In the mid-2000s, manufacturers also began to incorporate chambered designs into their windows, which break up the airspaces in hollow window frames into tiny spaces, in order to reduce or slow down convection. The end result includes U-factors that are light years ahead of older windows.

Knowing exactly how your old windows fall short and how heat is escaping will allow you to decide on the best measures for patching their performance.

Windows that incorporate multiple air chambers and foam fills help to reduce heat transfer via conduction and convection.


Step 2: Sealing up Window Leaks

If you determine that air leakage is a problem, depending on where it’s coming from, one of the easiest and most effective ways to stop those leaks is by applying caulk. But it’s important to note that you don’t want to apply sealants to parts of your windows and doors that are meant to separate or open. If you sense air leaking in around sashes (the “frames” that hold glass and typically slide up and down to open), then you can use foam gaskets to help seal them up. In those cases, you’ll want to consult with a home improvement retailer to find an appropriate product to cut to size and stick on where sashes come together or meet the sill. If air is seeping in around where your window frames meet trim, or trim meets walls, then a tube of caulk goes a long way to fixing those problems.

Chances are with a little sleuthing you can spot the cracks (typically dark lines, or crevices in paint between trim and windows) where you can apply a thin bead of caulk. Just follow the caulk manufacturer’s guidelines for application. It’s a process that you’ll quickly learn to master, but due to its messiness may also learn to hate. The good news is, a good caulk is rated to last as much as decades (though you should expect far less than what’s stated on the tube), so you won’t be doing this often.

This application of heat-shrinking plastic film is another option that tackles air leakage, while increasing the U-factor only minimally.

Plastic Window Films

Heat shrinking films seal up windows the same way that plastic wrap protects your leftovers—by stretching over your windows and sticking to the surrounding components to form a seal. The difference is, most plastic films for windows require a little heat to shape and adhere. The key here is ensuring that they don’t stop short of covering the full window system and thereby all of your leaky components. When possible, you also want them to stay separate from glass to form a layer of air. That’s where you get a slightly increased U-factor.

Most can be applied with a standard hair dryer, then trimmed to shape, but as you’ve probably guessed—don’t expect to get anything aesthetically pleasing. That’s not the point here. You’ll also have to sacrifice the option for opening windows on mild winter days, as well as will have to weigh carefully at which point you remove films in the spring. When you do remove them, you’ll want to be careful not to peel away paint or other finishes.

Great-Grandma’s Method

Probably the least effective method on our list includes “draft stoppers,” otherwise known as window snakes. This DIY measure has been around for as long as any of us can remember and is little more than a stuffed animal that’s often made of hand-me-down clothing and shaped like a snake.

When placed in windowsills where the window meets the sash, draft stoppers may provide some (some) reduction in drafts, but only when they’re kept tightly against the window, which is easier said than done. Even then, chances are they’re only going to slow or redirect air leakage in order to diffuse heat loss, rather than actually stopping it. The same can be applied around door sweeps, but in those cases you might find them a tripping hazard. In other words, of all the measures you can take, draft stoppers could be more of a trinket than an actual improvement. But hey, they’re a good use of an old shirt sleeve.


Step 3: Size up Your Window Replacement Options

Unlike in years past, when you had to pay an arm and a leg for the best performance, these days even the least expensive replacement windows provide impressive results. Tubes of caulk are inexpensive and therefore a no-brainer if you’re willing to deal with a little mess, but before you set out to purchase foam seals that might peel off and disposable films that have to be replaced each year, it could be worth a call to a local window dealer.

When you’re ready to begin the process, use to locate a reputable company to help guide you to an option that fits your budget. Within just a few clicks, we’ll connect you with a local company that specializes in door and window replacements.

Please note, this article may contain links to Amazon products. As an Amazon Associate, earns from qualifying purchases.


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