Low-E glass or window film: Which blocks heat better?

Window film installation should be relatively simple and take no longer than a day for a large house. (Photo courtesy of Advanced Film Solutions)

Window film installation should be relatively simple and take no longer than a day for a large house. (Photo courtesy of Advanced Film Solutions)

When the summer sun penetrates windows, your home's inside temperature rises — along with your cooling bill. Among your options to keep cool are installing low-E glass or applying a reflective film.

But, which works better?

Angie's List member Roger Linville submitted this question: "My front windows face southwest. I have no shade trees in the front yard, so I'm expecting my front rooms to get hot this summer. I also have condensation between the panes. I plan to replace the windows but am getting conflicting advice. Should I get low-E (low-emissivity) glass and rely on it to block infrared heat waves, or get clear glass and have an infrared-reflective film applied? Which will give me the best results?"

The majority of window professionals we spoke with pushed replacing windows with low-E glass windows. You get the best efficiency by replacing the entire window, because you also replace the frame’s weatherstrip and seal, says John Nelson, owner of window replacement company Austin Retrofit in Austin, Texas.

Most agree that window film blocks heat effectively, but aftermarket film comes with drawbacks.

Energy effecient windows

When looking at energy-efficient windows, look for two key performance indicators: the U-factor and the solar heat gain co-efficient. The U-factor indicates a window's overall insulating value; the solar heat gain co-efficient measures how well a window deflects incoming solar heat. An efficient window should be rated at 0.30 or below in both measurements.

MORE: How much does it cost to replace windows?

Mike Van Gundy, owner of Empire Window Co. LLC in Delaware, Ohio, advises that the low-E coated glass products that use an argon gas filling in between the glass are the best option.

For hotter climates, Mike Gilkey, owner of Gilkey Window Company Inc. in Cincinnati, suggests installing window glass with three low-emissivity coatings already built in. With LoE3, the triple stack coating goes on the exterior plate of the inside surface of the glass, so it's protected from the elements, which prevents it from tarnishing.

Energy-efficient windows will start at about $300 to $400 and could go up to $1,000. You may qualify for a federal tax credit by installing new, energy-efficient windows. (For more information, visit energystar.gov.)

Although pricey, experts say the investment will pay for itself over time.

RELATED: Consider your options when replacing windows

Window film effectiveness

Compared to low-E windows, the cost of installing tinted film on clear glass is less expensive overall. David Parke, a sales manager at Custom Sun Control in Marietta, Ga., says most solar reflective films start at about $6 to $14 per square foot. "For the money, you won't find a window that will give you the same performance as solar film," he says. However, installing the reflective film won't address an inefficient window frame.

Heat blocking window film also won't provide the efficiency of the newest triple layer low-E coatings that are sprayed onto the glass at the factory and then cooled to create a bond.

Applying aftermarket films to single-pane glass works to block infrared and ultraviolet light, but it's not a good idea with dual-pane glass because the film is applied to the inside of the window. Because of this, heat energy passing through the dual-pane glass is reflected back inside the insulated glass and can cause excessive heat buildup inside the unit, resulting in condensation.

Also, applying the film to a window may void the glass manufacturing company's warranty, because the film can sometimes cause seal failure in the glass.

Editor's note: This is an updated version of a story originally posted July 12, 2010.


Low-E glass typically costs about 15% more than ordinary glass, but it reduces energy use by as much as 30-50%, by using most of the heat gain in winter but keep the harmful UV rays out during the summer, and when used in insulated glass units – can have even better benefits. For hot climates, low-E coating should be applied to the outside pane of glass. If the windows are designed to provide heat energy in the winter and keep heat inside the house typical of cold climates, the Low-E coating will maximize benefit by being on the inside pane of glass. Low-e glass is recommended by many energy efficiency experts as a result of high performance combined with aesthetics.

My situation - I live in north Louisiana. I have 40 year old single payne windows with aluminum frames. Also, money is so tight now, new Low e windows installed in our home may run $10,000.00 No way I'm affraid. SO, that is why I found this sight looking for a Low E type window film to reflect the suns heat in summer and reflect my central heating and fireplace inserts heat in the winter. Okay, I think I got the reflection part down (if I can find the proper film at a good price,) now I need to block the traveling air in my window frames. I thought I would build a small wooden frame painted as the window frame (like window screen frame) and cover these with crystal clear vynil you can find at walmart or a fabric store. Then, I would put a 1/4 inch or so thick of weather stripping (to assist no air flow and to help hold the frame in place in the widow casing)on the outer edges of my frame work and make a small handle or handles on the frames to assist installing them in the window box frame. Anyway, hopefully a very functional/practable with little expense idea. Any suggestion to assist me, especially what to look for in Low E film? Thankfully, David

I would like to mention that a comment in this article is incorrect and I am not sure why Gilkey made such a statement. The paragraph discussing installing window film to dual pane glass..."but it's not a good idea with dual-pane glass because the film is applied to the inside of the window. Because of this, heat energy passing through the dual-pane glass is reflected back inside the insulated glass and can cause excessive heat buildup inside the unit, resulting in condensation." This is FALSE. Condensation is caused by water vapor not heat. Window film does not cause premature seal failure. Independent studies have been done to see if window film causes premature seal failure on dual pane glass and it has been concluded that the only issues that cause seal failure are poor quality of construction with the window and/or aging of a window unit. I have included a link to this study. Window film manufacturers will cover glass breakage and seal failure warranties for dual pane glass and dual pane low e if failure results after window film has been applied. (Do your research before selecting films. Not all films do.) I wish the writer of this article would have checked the facts before publishing this article. http://www.iwfa.com/iwfa/Consumer_Info/The%20Use%20of%20Window%20Films%20on%20Insulating%20Glass%20Windows.pdf

We installed Pella triple-pane insulated replacement windows with LowE glass in our house about six years ago (replacing single-pane windows which were literally falling to pieces) and immediately noticed that our upstairs was cooler. Our house also became a lot quieter because the insulated windows block more street noise than the single-pane ones did. We also hung light-blocking curtains in the bedrooms to keep out the afternoon sun. They've kept our bedrooms relatively cool and lowered the load on our AC. We've never used window films and therefore can't comment on whether they're better than LowE glass.

Like the majority of the emails we all receive from Angie's List, this one is the same: an advertisement masquerading as a PSA. The best treatment for your windows is to not have any windows. I do however plan on looking into the solar screens mentioned in a previous post.

I live in the desert with south facing windows, my house is 60+ years old. 2 years ago I replaced (retrofit) my windows with LoE3 with argon gas filling in between the glass My power bill for the summer fell by almost 75%. (also installed new A/C unit). If you live in a desert, buy the windows, don't use the film at the most use thermal blankets or better yet 2x thick curtains one side dark and one side light

Unfortunately, there is no single answer that will fit every situation for every climate. So the short answers is, "It Depends". As a provider of replacement windows, window film, and replacement of only the insulated glass units, we cover all options. In fact, replacing just the glass is another option that should have been included in this article. Bottomline, you will need to evaluate your current situation and then price out each option realizing that every alternative is a trade-off.

The best way to keep heat out of your house in the summer time is to install room darkening shades in your windows. Not only do they keep summer sun and heat out of your house, but they provide terrific privacy. In the north when winter comes all of the shades go up so the sun can heat up my house.

I had window film put on my southwest facing windows. Soon after, they started cracking.

They say there is a solar film that can be used with Low E windows? Will it cause the Low E to fail?

All Low-E is not created equal. Make sure you are getting soft coat low-e which is applied with a magnetic sputter process. It is actually a coating on the inside of the glass pack. I appreciate that there are plenty of amateurs willing to weigh in on film vs low-e but there is no impartial rating agency that uses the same ratings for both products. If looking at windows, you should focus on SHGC where the lower the SHGC the better. Windows can be expensive but go with a smaller contractor without a showroom and massive overhead and you can find a bargain. Sadly, many installers and carpenters do not understand efficiency. Just because a window manufacturer advertises a lot does not make their window a quality product. In northern climates you should make your decision primarily with u-factors in mind with the lower the u-factor, the better. Triple pane is always a better option. DO NOT ALLOW YOUR WINDOWS TO BE INSTALLED OR PAY FOR YOUR NEW WINDOWS IF THE NFRC STICKERS ARE REMOVED PRIOR TO DELIVERY AND INSTALLATION.

Please see the following official response from the International Window Film Association on this topic. It counters some of these misperceptions about solar control film. http://www.windowfilmmag.com/documents/newsiwfa20100722.pdf

window film is hands down the best. A top of the line film manufacturer warranties the window . Film manufacturers just dont have the money to spend on advertising that glass manufacturers do,LO E IS A WASTE OF PEOPLES MONEY !

C.Utrias, Your right no one answered the question. This is a difficult decision and we get a lot of customers asking the same question. As you stated there is a lot of conflicting information out there about window films and Low-e windows. It is good you are asking questions. My thoughts are if you live in southern climates where heat gain is a major issue I would recommend the window film and a clear IG unit because you will also have issues with glare and fading. Window films will block 99% or more the UV rays (main cause of fading) and an overwhelming number of Low-e windows will not. If you live in northern climates and cooling is more of an issue the Low-e window will probably have a better result. You can always add window film on windows only apply it to those selected windows. Window films now are safe for Low-e windows and if a warranty is voided by applying window film the window film manufacturers will take over the warranty for glass breakage and seal failure. I will mention that I am a window film installer in Central Texas for 16 years. I work very closely with glass companies throughout Texas. Low-e windows are nice but we have found that customers still want window films in addition to Low-e because it isn’t enough.

If the reader’s goal is to keep the heat out during the summer, clear glass or tinted glass with solar window film is definitely the best option. My suggestion is based on my experience as a Vista Window Film dealer in Colorado. First, I must clarify some misconceptions about window film that are included in the original article. First, most window film manufacturers have substantial warranty periods and in the case of Solutia Performance Films premium brand – Vista – the consumer can choose the Gold Warranty which matches the window manufacturer’s warranty for a small additional cost. The second unspoken assumption that I should clarify is that some window films are also eligible for federal tax credits. You can find more information about window film tax credits on this website: http://windowfilmtaxcredit.com/ Now, to answer the question: which blocks heat better – low-e glass or window film? In order to conduct an apples-to-apples comparison between low-e glass vs. solar window films, you will need to know the heat reduction specification for the low-e glass (not all low-e glass has the same performance) and the cost of both low-e glass and clear glass with window film installed on it. Here are the steps I recommend taking to conduct an accurate comparison: 1. Have a glass company provide a quote for windows with clear glass and a quote for windows with a low-e coating, and make sure to get the performance for that low-e coating. 2. Contact a local Vista window film dealer and have them provide a quote for the installation of a solar window film, and make sure to get the performance of the film. Find a dealer at www.vista-films.com 3. Then, you can compare the costs and performance between the two options. Lastly, window films offer many benefits in addition to keeping you cool in the summer. Vista Window Film can reduce your annual cooling costs up to 50%, it provides 99.9% UV protection that helps prevent skin cancer and interior fading, and it offers safety by holding the glass shards together in the event that a window would break. And if you are looking to reduce energy costs all year, the new Vista EnerLogic low-e film series offers year-round insulating performance for your windows. You can keep the heat out in the warmer months and trap it in during cooler months. www.enerlogicfilm.com

After buying the best low-e fiberglass windows, I found Inflector solar selective window insulators. Basically it's an energy screen that reverses in winter to become a passive solar collector. Also cuts out infiltration when mounted as an interior panel. Why buy new windows? These at least double the energy efficiency of a window, according to Texas A&M testing. Cut UV, reduce glare, reject infrared heat. Great product.

Did you buy the inflector blinds. Are they effective?

low e windows are a good investment in the midwest or east coast but in the southwest the best cost for the money is a good dual pane with at least a 1/2" air space Install a high quality solar control film with a high total solar rejection and it is possible to reject as much as 80% of the heat gain it also helps keep the heat in in the winter time I have been in this business for over 30 years an am registered with the IWFA as a Solar Control Film Specialist.

Comment on the tax credit. We replaced 4 windows last year with the best triple pane and again this year put in four more thinking we would get a tax credit. Unfortunately we don't pay enough taxes (because we don't make enough money). No one told us this little bit of information when we were purchasing the windows. It's hind sight now but thought some would like to know this info before getting anything that says a credit if available for a product. (We're senior citizens) But the credit was an incentive to purchase when we did. I looked up tax credits and could fing no restrictions. The bottom line is, there are restrictions.

THe newer low-e glass is very effective in reflecting out extra heat - summer AND winter! Film has the same issue - I would recommend neither and use drapes or blinds that are closed when the sun is broiling your house!

We chose double pane, clear windows for the south, but low E for all other areas. We chose an expensive brand, Accurate Dorwin of Canada, because no one in the US offer pultruded fiberglass, insulated frames with the quality of glass we wanted.For the view I didn't want any low-E. Now we're going use temptrol curtains from www.radiant barrier.com to reflect the summer heat from the south and save our internal heat in the cold winters.

Where is the common sense in this? Of course window contractors are going to try to sell you replacement windows versus the film! What they don't tell you is that modern windows are designed to last a maximum of 20 years, so you would need to replace them AGAIN! Frequently the older windows, made with hardwood no longer available, were built to last forever. I know because I live in a house built in 1886 with its original windows.

The cheapest solution to solar gain for south facing windows is to hang a space blanket (costs $1-5) with the shiny side facing out. This blocks 90% of the heat gain, although it can look somewhat tacky. I have this on 75% of my windows, so I still get some view. I also applied it to 50% of my skylights. Space blankets, also called mylar or thermal blankets, are available through camping equipment stores and army surplus stores.

Another good option is awnings. They can block the summer sun, which is high in the sky, but let in the winter sun, which is lower.

Nobody answered the question! They are already replacing the windows.... the question was replace with either low e, or clear with film....

I like my windows, if replaced my cats wouldn't have their beloved ledges anymore. I've looked at film but it is very expensive. I'd like to reasonably priced film to put on old windows and settle for less efficiency and huge replace bill.

I have a little understanding about saving energy...consider putting SOLAR screens (full window coverings) that have swivel lock keepers so one can remove them in the winter to help with solar heat gain. These are by far the most economical way to reduce heat light from coming into one's house!

I'm sure that replacement windows would be a more comprehensive solution, but the cons of film aren't really an issue for most. If you're already thinking of replacing your windows, they're probably out of warranty -- if they were ever "in". Mine are 90 years old. Storms have been added, but they are still pretty leaky by new window standards. And condensation is the least of our worries for those of us in the "ancient window" situation. I've also noticed that it seems to rather dramatically increase the cost to specify replacement windows that match the appearance of original hardware, so there's another tradeoff. If I had sufficient funds, and I thought I'd surely be staying in this house for 20 years, I'd go for replacements. But lacking those, I'll adopt a more "provisional" solution.

We owned a 50+ year-old home that still had its original single-pane windows. Money was tight, and purchasing replacement double or triple-pane windows was not an option. We put window film on all our windows that got the most heat. The window film is certainly a viable option for those who want to block some heat, and it doesn't cause any of the problems the contractors were talking about that happen with the newer windows. It might not be the perfect permanent solution, but it is certainly more affordable if you need something more affordable. I also agree with what Barbara said - solar shades are a great option as well. And again, if you're looking to save some cash, there are heat and light-blocking fabrics available at your local fabric store for a fraction of what you might pay for a brand-name solar shade.

Some of the double pane windows in my home are 'cloudy'. Initially, I thought they were just dusty/dirty and tried to clean them; both on the outside and the inside. No luck. It appears that the film is on the inside between the 2 panes of glass. It doesn't appear to be condensation; it appears to be more of a constant film. Is there a "fix" to this or do I need to begin replacing the windows in my home?

Window coverings also offer an additional layer of insulation from heat gain. Honeycomb shades, such as Hunter Douglas Duettes and Applause product, actually carry an R Factor against heat loss and also help to keep heat out. These elements provide 95 - 99% UV protection and offer a very low profile on the window as well. Solar Shades are another low profile but very effective method of dealing with heat. The darker sun shade fabrics allow a clear, crisp view to the outside as well. While they do not provide privacy at night, they do reduce heat gain, especially if the solar fabric has an aluminum-coated side facing outward, as this reflects the sun instead of absorbing it as other dark sunscreen fabrics will do. Hope this helps.

I feel this article was very biased toward the glass manufactures. And some of their information is inaccurate. Window film does not harm properly constructed windows. When you look at the overall performance, value and the effect on the environment window film is dramatically more environmentally conscious.

We had double pane replacement windows installed a couple of years ago. In the summer, they have a huge amount of condensation on the outside in the mornings. In the winter, there is huge condensation on the inside in the morning. We have our AC at 70 in the summer and the heat around 65-68 in the winter. What can we do to eliminate this condensation? I've tried to contact the distributor and the manufacturer and get no response. Thanks!

Make sure your Ac vent blows on the window to get the condensation off it and run you fan on program or on for a bit to see if that slows down the condensation.

Another factor to consider for those of use concerned with environmental impact. A better environment inside and out.TM Bekaert Specialty Films today announced its flagship Solar Gard® and elite Panorama® architectural solar control window films produce a net reduction of greenhouse gas (GHG) emissions. They are the first building improvement products made in the U.S. to measure and report their carbon footprint.1 By reducing the amount of energy used to cool commercial buildings and homes, Solar Gard and Panorama window films help decrease carbon dioxide levels in the atmosphere and help achieve zero energy building goals. Solar Gard window films are carbon negative in all 50 states and across the globe. On average, they are carbon neutral within one year of installation. More efficient than low-e coatings at rejecting solar heat, Solar Gard window films are both carbon-effective and cost-effective, reducing a building’s carbon footprint more effectively and for less money than new windows. In fact: • One square meter of a low-e wood window, the type with the smallest carbon footprint, has a carbon cost of 253 kilograms. The carbon cost of Solar Gard window film is less than one kilogram per square meter.2 • Solar Gard window film saves 1001 times more GHG emissions from entering the atmosphere than is used and/or created during its manufacture.3 • Solar Gard window film installed between 2007 and 2008 saved 3.6 million tons of CO2 from entering the atmosphere; this is equivalent to the carbon output of 16,350 American families (with four people). Solar Gard’s impact on the reduction of global carbon emissions is enormous because heating and cooling systems in buildings produce significant levels of GHG emissions.4 Improved 1 According to EPD registrars, www.climatedec.com and www.thegreenstandard.com 2 2009 Buildings Energy Data Book, published by the U.S. Department of Energy 3 Global average; for regional variances please contact :Jami.wong@bekaert.com Press release May 19, 2010 Solar Gard® Window Film Cuts Carbon Emissions Worldwide First U.S. company to achieve Climate Declaration for a building improvement product; Solar Gard calls for an end to “greenwashing” claims that mislead consumers Media contact Colleen Sheehan 978-499-9250 x 227 bsf@matternow.com fenestration can lower energy consumption and GHG emissions by 10-40 percent in both commercial buildings and homes5, and an installation of Solar Gard window film transforms standard glass into high performance windows. End to Greenwashing Many companies claim to save energy and reduce GHG emissions without factoring in the environmental cost of their raw materials, manufacturing process, distribution, disposal and recycling. A complete lifecycle analysis is a required component of a Climate Declaration, and for Solar Gard and Panorama architectural films it meant that the total carbon impact of the films on the environment could be measured. “We believe companies shouldn’t claim to be green while hiding how their products are made. They’re simply greenwashing consumers if they do. Consumers deserve to know the real environmental impact of the products they buy,” said Christophe Fremont, president of Bekaert Specialty Films, manufacturer of Solar Gard and Panorama window films. “If a product claims to save energy then it should be mandatory that they publish the full impact the total life cycle of the product has on the environment, and consumers should demand to see this information.” How the Climate Declaration was Performed BSF invested more than $1 million measuring and certifying the company’s carbon footprint, updating its environmental management systems and performing the lifecycle analysis required for the Climate Declaration. The company’s cross-functional team spent more than a year collecting and analyzing data, following ISO 14025 standards. Two independent organizations, Alta Nova, LLC and Five Winds International, reviewed and audited the data before it was registered with The International EPD Consortium®. Solar Gard’s Climate Declaration is available for download at http://www.solargard.com/Assets/PDFs/BSFClimateDec.pdf. About Bekaert Specialty Films Bekaert Specialty Films, LLC (BSF) manufactures and distributes window films that provide solar control, energy savings and CO2 emission reduction, safety, security and glare reduction solutions for architectural and automotive applications. They are sold in 60 countries worldwide under the Solar Gard®, Panorama® and Quantum® brands. BSF also manufactures films for the photovoltaic, electronics, medical, graphic arts and imaging industries. Committed to environmentally responsible manufacturing, BSF works with the Clinton Climate Initiative to reduce carbon dioxide emissions, has certified its company carbon footprint to earn the title of Climate Action Leader, and its manufacturing facility is ISO 14001:2004 and ISO 9001:2008 certified. Headquartered in San Diego, BSF is a subsidiary of Bekaert (Euronext Brussels: BEKB), a global company based in Belgium whose annual combined sales are €3.3 billion, more than $4 billion. More information is available at: http://www.solargard.com/Energy/Home 4 Pew Center on Global Climate Change, http://www.pewclimate.org/technology/overview/buildings 5 Ander, G. D. “Windows and Glazing”

Any heat that comes through the window will stay inside unless it is reflected back out.

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