Window film (for energy saving) questions


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Old 03-13-23, 01:37 PM
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Window film (for energy saving) questions

Background: I've been reading as much as I can about window films for my situation, which is: Sunny Florida, 3 side by side 3 foot (38 inches to be more precise) wide/7.5 foot tall sliding glass doors (total 9 feet wide 7.5 feet tall) facing South (not double-pane) where the full left to right top to bottom of these doors is in direct sunlight, in the biggest living area of the house (largest to be cooled) and miserably high electric bills in the summer.

I do have some thick light-blocking curtain liners in place already. I know they help a bit, so my questions are to try and see if adding window films also might help a bit more.

I don't want dark tint necessarily, the view is very nice out those doors, I don't want to lose all of it, but I want something that might reduce the electric bill somewhat. (Replacing with three huge double-paned sliding glass doors isn't in the budget right now.) I've been mostly looking at reflective film, but I'm open to suggestion too.

My question(s)
  1. First, a disclaimer: I'm not expecting magic, just wondering if some form of solar-shielding window film will be worth the lost weekend and money putting it up.
  2. My biggest question, is what knowledgeable people think: Starting with reflective solar film and reading various online reviews, I see some greatly conflicting reviews and opinions, ranging from "it worked incredibly well" to "the window surface got so hot, the radiated heat from the now hotter glass was no improvement over (without film) the radiated heat that previously heated up the floor tile." It seems like both things can't be true at the same time. Opinions?
  3. Other suggestions?
Thanks in advance.
 
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Old 03-13-23, 02:12 PM
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I believe a reflective coating on the outside of the glass is best for rejecting the sun. This reflects the light before it enters the glass. Unfortunately it also happens to be the most ugly since it makes your windows look like 80's mirrored sunglasses and it doesn't hold up very well since it's outside and exposed to the elements.

Films applied to the inside of the glass don't work as well in some regards. For one, the light must pass through the glass and be inside the home before it ever encounters the film. To block UV most films convert UV to IR (heat) so the film can get quite hot. And depending on the darkening level all the light energy being blocked by the film gets converted to heat. Any light reflected by the film must pass through the glass a second time, further heating the glass. These films often just have a darkening gray or amber but reflective ones are available. Since the film is on the inside it can last much longer than film on the outside.

There are also perforated films. This is a thicker vinyl with tiny holes punched through. These are used for restaurant signs and for wrapping taxi's and busses in advertising. The holes let you see out but the solid part of the film blocks the light. The film is available with different amounts of open area to control the light that enters the home. Plain white is good for staying cool and and makes your windows look white. I do not recommend having the film printed or colored as the dye's will eventually fade.
 
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Old 03-13-23, 03:38 PM
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Cant speak for the solid ones but a house we had back in the 90's had a den with very large window as well as circle top facing South meaning it got summer sun all day.

I installed the film myself, do not recall brand/color/style but it really made a difference in the amount of light entering the room and I dont recall it ever having a look on the outside that made it look odd.

Long story short, contact some local window film installers and see what they have, hopefully the products are much better today than 30 years ago!
 
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Old 03-14-23, 10:36 AM
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Would a roof or canopy over the doors be in the budget?
 
 

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