Window Film : Fact or Fiction?

[sharp]

Like many folks, I probably could use new windows (15 year old house, double pane aluminum, some of the seals have broken). Question: Does anyone have experience with Window Film (made by 3M corporation, installed by folks such as "Solar Tex", etc). Any insight, good or bad, will help me determine if it would be a good investment vs. replacement windows ($XXXX for windows, >$XXXX for window film). Thanks in advance.
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[Edited by Mod2 on 12-28-2005 at 09:40 PM]

[duff beer]

I still have 3 double pane aluminum sliders (soon to be replaced) and live on the Canadian prairie. I use window kits on those windows and it makes a tremendous difference. The rooms are far more comfortable and the windows don't ice up (all that much, lol) when it gets to -40. If you are unable to replace the windows then the kits are a cheap, easy fix for the winter.

[RoBoTeq]

I think the OP is talking about window tint which does make a difference for cooling. If this is about the plastic window covers; they look terrible but if installed properly do a good job.

[perel]

I work in a 9th floor, southern exposure, wall-o-glass office. Solar film was installed last year. Before the film, I had to run my air conditioner (supplemental PTAC heat pump) constantly in August and even a fair amount in January. Now, with the film in place, I don't have to run the a/c constantly in August and even occasionally need a few minutes of heating. I'd never used the heat through a full "heating season" without the window film.

The film is visually noticable. It's kind of like wearing sunglasses, but less so. I can definitely see a grey/brown cast to the clouds, not much of one but it's there. I can also see more of my reflection in the window than before, and from the outside the glass is MUCH more reflective.

One other factor which may or may not be a consideration in your area is that the film also adds shatter and "smash and grab"/flying debris resistance. Nice to have if you're in hurricane country.

I am going back and forth myself about getting window film for my house. It certainly would help with cooling - Man J estimates several thousand BTUs of reduced sensible load - but I'm not sure about the visual impact.

[sharp]

Thanks to all who have offer their comments. However, Does anyone know if the film has any indoor heat retention qualities, or is it good for defleating the sun's heat during the summertime.

[operator]

its good for reflecting the suns rays away from the house, sort of like drapes prevent the radient heat load from getting in.

indoor heat retension, film doesnt help

you would be further ahead replacing the windows and preventing the air exchange. put up blinds after the windows are done and that will help

[perel]

There is more benefit for cooling, but some for heating as well. Depends on the exact film you choose.

From 3M's website: ( http://www.3m.com/us/arch_construct/scpd/windowfilm/ )

Our films reduce up to 99 percent of the sun's ultraviolet rays and reject up to 79 percent of the solar heat that may otherwise come through a window. They also help reduce winter heat loss by reflecting up to 35 percent of indoor heat back into the room.

Do keep in mind that the film is going to significantly reduce winter solar gain, so you're not going to benefit from passive solar as before. Might be a net negative, don't know enough about your house to say.

[dryguy]

Windows lose heat two ways. The first way is through conduction in which the heat travels through the material to the outside. R-factor is the resistance in the materials to let the heat pass. By adding the film, you gain heat-loss resistance from the material itself and also there is added heat-loss resistance from the dead air space between the film and the window-- bonus.

The second is through radiation. The trasnparency of the glass allows heat to radiate out of your house. There are window treatment films with low-e (low emissivity) qualities that slow down the heat loss due to radiation.

When shopping for a product, r-factor and emissivity what you will use to compare products. Good Luck

Dryguy

[on call]

There is a lot to selecting the right window than meets the eye (pun?). In the world of load calculations, windows falls under the heading of fenestration. When looking to buy windows for a pearticular function (less heating load, less cooling load, etc.), the window (glass doors included) should be rated according to the National Fenestration Rating Council (NFRC).

Depending upon the glazing: tinting, reflective coating, low-e coating, etc. the manufacturer tailors the window performance to the climate by controlling what part of the thermal spectrum gets through the window.

Here in the South, we are a predominately cooling climate and therefore, glass needs to stop the infrared energy from getting in the room. Tinted and reflective coatings can do this, but at a reduction of Visual Transmittance (VT) and thus reduce the clarity of the glass (window film is a good example). Low-e coatings seem to be far superior in that they can be engineered to tailor the glass to the climate while still having a very good VT value.

The point I'm trying to make is that you must determine what function you want the windows to perform: reduced heating, reduced cooling, or a balance. With this in mind, you can compare how the window performs with other windows. I would have a lenghty discussion with a window dealer (NOT a DIY employee like at Lowe's or Home Depot) who really can guide you in the direction and give you the best solution for your money because windows can get rather expensive and have a large impact on the heating & cooling load on a house.

[operator]

How many people would put a VS fan on a 15 year old furnace to increase efficiency?

[perel]

I don't think that's a reasonable comparison.

Yes, the tightest envelope is generally going to be new windows. That's expensive, though, and the payback often isn't there when the old windows can be repaired to perform almost as well.

When it comes to historic wood windows, I'm also a preservationist - but even with windows of no historical significance, caulk and storm windows can get you most of the way there for MUCH less money. Well-caulked and weatherstripped old windows will have less infiltration than hacked-in new windows, and won't leak much more air than well-installed new windows.

It's very illuminating to run a Man J twice, same house, same design conditions, and just change the window types. Storms give a huge benefit over single-pane alone; every window improvement above "single pane with storm" provides much more modest savings. Unless there's a major deficiency in the U-values MJ7 uses, I just don't see new windows as having an impact proportionate to their price.

New windows certainly have their place. If the existing ones are builder-grade junk with bad seals, and you're going to replace them with higher-end ones, great. Once you've paid for new IGUs as the seals fail, you're getting expensive enough that you might as well spend a bit more and have nicer windows anyway.

There are plenty of good reasons to replace windows. In and of itself, utility savings aren't going to be it. If I had failed IGU seals, I'd probably either put up heavy curtains or replace the windows entirely. Depends on whether the windows would ever be used anyway - curtains certainly are a lot cheaper, but they preclude using the window.

[cem-bsee]

film will not equal benefits of dbl pane --

an alternative would be to add storm windows over existing.

for better answers, get the load calc from this site & "play"

I use film by Gila, mainly for summer, only on west facing windows (I have no south facing windows) -- but, even the slight tint decreases the visiblity = grey or gold.

[sharp]

So, in summary, I think I'm hearing that Window Film will provide significant benefit in the summer, and some benefit in the winter, but there are other alternatives to consider. However, when you do a cost-benefit analysis, the window film will pay for itself, but should be regarded as a short-term investment???

[koald]

I have some of the same questions as Sharp and I appreciated On Call and Perel's informative responses.

[cem-bsee]

ROI of window film: short if you take it off in the winter to gain heating --
some of my Gila film has been in place for 4y now.

2 y/a I removed film from patio door for plants -- did not do that last yr -- PIA to clean adhesive off glass -- not bad = ~1.5h, PIA to install new & $30 of film --

I have film on seven 3x5ft combination storm windows, one 3x3ft window, one 2'8 storm door, one 6ft patio door which has dbl pane glass -- Yeh, Gila states not to install on storms, nor over dbl pane, but I was not about to cut small pieces of film to fit the upper wood window sashes with 6 lites ~10*12" ea.

BTW, my 1974 wood windows are well weatherstripped! channels are alum with plas inserts -- plas is crumbling, but seals still work -- at least the builder did not cheat there -- [ could not hang doors plumb! ]

[jfs1138]

I have put the Gila film on my sons bedroom south facing windows and it definitely helps reduce the heat gain in his room in the summer. It's not a miracle, but it does increase comfort and reduce some load on the AC in there. For that sort of thing I think it's an excellent choice.

I started preparing to do it all around a big sun porch like room here (used to be an indoor swimming pool, previous owners filled that in and put down nice tile it's the family room now) but I have decided to go with removable solar screen on the outside so that i can remove them in the winter time. I'll get to building those as soon as I figure out where I'll store them in the winter time...

[sharp]

Thanks for everyone's input. I appreciated this discussion and hope everyone else has, too.