Interior Window Insulation Methods -
Easy and Effective, and Economical



Window insulation can perform wonders for tired windows. If you have double-paned (and even single-paned) windows that are structurally decent, you can increase their efficiency to rival and in many cases, surpass new windows by installing interior-mount window insulation.

Replacing windows can be very expensive, often costing many thousands of dollars. But the alternative of having old, leaky windows is an even greater liability to your pocketbook and comfort. Consider a very legitimate alternative: affordable insulated window techniques.

Simple Interior Window Insulation Methods That Work

Effective window insulation prevents heat loss and helps regulate the surface temperature of the interior glass. Once you eliminate the heat loss from leaks or convection, insulated windows ensure an even temperature throughout the interior of the home, increasing energy efficiency. They also make it possible for heated homes to maintain a higher humidity level, therefore, better air quality, and reduce the risk of condensation on the windows. Here are some common methods to insulate your windows from the inside:

  • Plastic insulating film - There are a few different variations and film products.

    One type is the inexpensive window insulation kits at hardware or home-repair stores. The kits come with a large sheet of plastic film (I have seen people use plastic or shrink wrap or even store bought plastic sheets) and a couple of rolls of double-sided adhesive tape.

    Stick the tape around the window frame on all four sides, then mount the film on the tape so it completely covers the window. The film will block all access to the window, so if the window has Venetian blinds, cut a little hole while mounting the film and sneak the control rod through so the blinds can be opened and closed. Cut the excess film away with a knife or scissors.

    For the shrink wrap type, you will need to use a hair dryer to blow hot air at the film so it tightens and makes a firm seal with no wrinkles.

    A few caveats and tips: if looks are important to you plastic window insulation is not the most attractive strategy but it works well.

    If the tape is too old (more that 2 seasons), it will not adhere to the plastic sheet well, or it may separate from the wall or the plastic at some time during the season. This has happened to me enough times to make me gladly pay for a more expensive kit to ensure the tape is sound.

    Make sure that the surface which you will adhere the tape to is clean and dust-free. Be careful not to blow dry too long - if the sheet is stretched too tight, it will separate from the tape, maybe not immediately but definitely during a cold night, when it shrinks. That's why I suggest cutting the plastic larger than the window, leaving a little extra on each side; it may not look good, but at least you will be able to re-fasten it.

    Another type of "insulating film" is the self-adhesive type that clings or sticks to the window glass itself. This film is generally tinted and while it has insulating properties by helping reflect heat inward or outward (depending on how it's applied)and creating a small air gap, it also serves to protect against UV (ultra-violet) rays. 3M is one brand that provides this product.

  • Interior mount window insulators - These are essentially interior storm windows. They are by far, the most effective means of upgrading existing windows, while maintaining visibility, and visual appeal.

    Interior window insulators can be made of a wood or an aluminum frame with dual glazing films that create an insulating airgap in addition to the air gap that is created between the unit and the window itself. The unit is lightweight and mounts on the indoor side of existing windows or sliding doors.

    Weather-stripping is used as a seal to eliminate drafts and create a thermal barrier. The weather-stripping also creates a vapor barrier that stops condensation (causing peeling paint, rotting woodwork, and mold).

    This technique can improve window insulation values of existing windows to rival or surpass the highest U-values of any windows on the market and can save as much as 55% on annual heating bills. This is a particularly good technique for historic window preservation, since it doesn't usually require special permits, and can be made to mimic the look of the period.

    There are a number of companies that produce interior-mount window insulators, but they are usually made to order. Very few have installation services available; typically, you have to measure your windows yourself (I recommend more than twice, cause mistakes are costly), and install the insulators yourself, unless there is a network of installers in your area. You can also make them yourself with a wood frame and two thin, rigid plastic sheets, making sure that all parts are well sealed.

  • Insulating drapes and treatments - Curtains, shades, and blinds not only serve as a beautiful interior design element, but when backed with insulation material they can add a great deal to air sealing and insulating of windows - provided they are properly installed. Window insulation with window treatments doesn't depend so much on the heaviness of the material but the tightness of the seal.

    The objective of this type of window insulation is to prevent the room air from circulating into the space behind the curtain. Weights, magnets, Velcro, snaps or staples can be used to make sure no space is left between the drapes and the window frame, windowsill or floor.

    You can insert effective thermal shades while leaving existing drapes or shutters in place. Do-it-yourselfers can make them at a fraction of the retail cost, and have the flexibility of choosing their own fabrics, insulation quality, hardware and finishing touches.

  • Insulating at window sashes - The challenge here is prying off the molding that surrounds the window frame. Once that's done, it's relatively simple to measure a piece of rigid insulating foam to fit into the space between the window jamb and the wall, and spray a substance such as expanding polyurethane into the jamb itself. Or, you can easily use expanding spray foam.


  • Bubble Wrap - This is a cheap-but-fantastic window insulation trick for windows that aren't in the public eye. Use a spray bottle to mist some water on the interior of the window, and slap the packing material on, bubbles against the glass. Bubble wrap can stay up for months with no other adhesive, and may double the insulation value of a single-pane window. It also allows for gentle light to be filtered through with built-in privacy.
  • Water Walls - This insulation technique is sort of a throwback to the 1960s, when water columns were used behind southern-facing windows (or any windows that receive a good portion of light and heat during the day). These water columns were used to capture the sun's heat during the day and store it. The heat would then release at night, tempering the air, and reducing large temperature swings.

    The same concept of heat storage (or thermal mass) can also be used with other types of material, such as a paraffin or wax, a concrete slab, or even a black-painted storage container filled with rock or gravel, that can capture heat and then have it released using an air circulation fan. Unfortunately, water columns can give rise to algae.

    Architect, Michelle Kauffman has demonstrated a novel and simple method to get the heat storage benefits of water by creating a shelving frame that is installed inside a window and can store water bottles. These bottles can be decorative or tinted, or you can use simple mason jars that stack neatly on the shelves.

    The beauty of this method is that you can change out the bottles, replace the water, or control the amount of filtered light coming in by inserting different plants or flowers or other objects inside the bottles (see photos).

    water wall serving as window insulation





Return from Window Insulation to Efficient Windows

Return to HomeEnergyFaire Home

Search this site or the web: