I'm curious if tests have been conducted to evaluate the energy efficiency gains and resultant savings produced by insulating window films like these 3M Window Insulator Kits. (There are also films that are adhered directly to window glass that block UV and such; I'm specifically talking about the kind you tape on to the window frame to seal leaks and create an extra pocket of air.) The bottom of that page states:
Using a 3M window insulator kit can save up to $18 per window this heating season. Values based on averages from the northern half of the United States. Actual energy savings are subject to change and will vary depending on furnace and window type, average indoor/outdoor temperature, length of heating season and other factors. Savings based on energy costs as of August 2011.
I'm curious if tests have been conducted to verify these claims. Perhaps the best and most practical/useful way to go about the question is:
For the average house (# of windows, type, size, heating costs, etc.) in the northern US, is the cost of the window film (ideally more) regained in energy savings?
Let's assume that the kit costs $15 and insulates 5 windows (but 8 windows should be treated like two kits ($30), not $15 kit/5 windows per kit x 8 windows = $24).