Should Plastic Wrapping Go on the Outside of Windows to Conserve Energy?

Plastic will reduce lost heat and your heating bill.

Placing a plastic wrapping over a window can drastically improve the energy efficiency of the window, cutting down on drafts and the amount of heat released from the home. While plastic can technically be applied to the inside or the outside of the window, there are several important things to consider before installing the plastic.

Outside Applications

Plastic film can be applied to the outside of the window, but the disadvantages of doing this should be considered before application. While the film is durable, it will not be able to stand up to many of the elements that can buffet outside-mounted film during the long winter months. Something as simple as a nearby tree branch blown by the wind can tear the plastic and render it ineffective. Plastic that is exposed to low temperatures can become stiff, making it more likely to break or tear. Once this happens, it will be more difficult to fix plastic on the outside of the window than plastic installed on the inside. Plastic that is ripped beyond repair can be extremely difficult to replace when mounted on the outside of a window.

Inside Applications

Installing plastic on the inside of the window will protect it from the uncontrollable elements outside, as well as from freezing temperatures. Mounting plastic on the inside will make it easier to replace should it be damaged. It will also be easier to reheat the plastic with a hair dryer to remove any wrinkles that might develop as the plastic stretches and sags. Plastic that is damaged beyond repair can easily be replaced when mounted on the inside. Depending on the type of adhesive that comes with the kit, it may adhere better to an inside surface than an outside.

How It Works

The plastic stops the heat from leaking out around improperly sealed windows and minuscule cracks, but it also prevents heat from escaping through the window itself. When installed on the inside of the window, the plastic prevents a large amount of the heat transfer from the room into the glass, allowing the glass to remain cold. Alternately, plastic on the outside of the home will not keep the glass from heating up, wasting energy that would otherwise would not be channeled into warming the glass windows. Plastic mounted on the inside is also more likely to help prevent moisture from building up.

Other Alternatives

Several other options can present viable alternatives to mounting plastic wrap on the outside of the house. If it absolutely can't be mounted inside the window, using caulk or other types of sealant around the window frame can help limit drafts and heat loss. Sturdier options such as window treatments and shades can be effective when mounted on the inside of the windows. Interior window panels are also an option; these panels sit inside the windows that are already in the home, providing another layer of insulation and helping to stop air leaks.

References

• Kansas State University: Building Envelope: Infiltration
• Building Green; Improving Your Windows With Plastic Film Kits... ; Tristan Roberts; August 2011
• Lower My Energy Bill.com: Plastic Window Insulation Film
• Planet Green; Conserve Energy With Plastic Window Insulation; Josh Peterson; February 2009