Do Insulating Window Kits Work?

by Erik North on June 27, 2012

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In case you can’t tell, I wrote this in November just as I was hanging up my 3M window film. Just wait for my January posts on the best window mounted air conditioners!

Everyone knows about insulating window kits. They’re simple cheap, effective and most people avoid them like the plague. Plastic window insulation kits may work but they commit the unpardonable sin of looking unattractive.

But compared to most other ways of improving window R-value and performance, the window insulation films provide the most bang for the buck. They may not be attractive, but they outperform most other window insulation options especially in stopping drafts and preventing condensation.

What is Window Insulation Film

Window insulation film is a ubiquitous, low cost way to improve your window’s insulation and reduce drafts. It consists of a clear oversized plastic film designed to fit over the interior of a standard-sized residential window.

The kits usually include double-sided tape to adhere the plastic around the edges of the window frame. Once secured on all four sides, applying heat from a hair dryer or other source will shrink the plastic, tightly sealing the window.

R-ValueThe R-value of windows is usually expressed as U-Value, which is simply the inverse of R-value. The U-value of most windows is either 0.49 (about R-2) or 0.35 (around R-3). By comparison, a modern wall assembly can be R-20 and up. The windows are by far the weakest thermal point in the wall assembly. And since windows are either a) not much better (vinyl replacements) or b) too expensive for the payback to merit the cost, we look for less expensive alternatives that deliver some of the same benefits. Luckily, we’ve been talking about one for the last 400 words.

Plastic window films are obviously very inexpensive. And they do add approximately 1 to the whole window’s R-value by trapping air between the plastic and window.

As an added heating benefit, when clear window insulating film is applied to south facing windows, it allows in the sun. This natural heat gain reduces how hard your heating system works. Insulating curtains are a similar product often used for windows. However, they miss out on the solar heat gain as they’re blocking out the sun.

Air Sealing – Homeowners rarely complain about cold, uninsulated walls. They’re cold but who cares? As long as the homeowners aren’t hugely impacted … whatever. That changes a great deal when cold air drafts are involved. Cold air blowing across your neck and feet draws immediate attention. And all too often this leads to a window replacement appointment.

Insulating window films seal to the window frame. This stops all the air leaks around the window molding, frame and eaves. Stopping this air draft makes a huge comfort difference as homeowners no longer feel those cold fingers of air across their neck.

Price – How can you beat the price? Not with a large stick. Insulating window films are about the least expensive way to improve R-value and comfort in the home.

Improving window R/U-value is not easy or normally cheap. Replacing windows with genuinely more well insulated ones can be prohibitively expensive and adding storms is less expensive but less beneficial. The plastic films address air leakage, add some insulation, let in the sun for only a few dollars. And all you need to do is tolerate that they’re a bit ugly.

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