I’ve talked about the Different Types of Glass before and their relative energy efficiency but I wanted to dig into Low-E glass a little today so you can see if it is right for you. I get a lot of questions about making old windows energy efficient and when the temperatures start to dip the questions ratchet up.
Low-E stands for “low emissivity” and has become a standard material for windows and doors since it first arrived on the scene in earnest in the 1980s. Emissivity refers to the amount of heat that the glass is able to emit. So, a low emissivity glass will emit less heat than one with high emissivity. It works by blocking certain wavelengths of light but allowing others through. The sun’s light comes in a few forms and they each have a unique range of wavelengths.
- Ultraviolet Light (UV) Wavelength: 310-380
- Visible Light (VL) Wavelength: 380-780
- Infrared Light (IR) Wavelength: above 780
Low-E glass attempts to block high amounts of UV and IR light while allowing as much Visible Light in as possible. I could get very science geeky here but Low-E glass is basically good at preventing heat from passing through it. In the summer it keeps the heat from getting in and in the winter it keeps the heat from getting out.
The Low-E coating is a micro-thin layer of reflective materials like tin or silver that is applied to the surface of the glass. So knowing which side is coated is imperative to good performance. In single-paned applications you always want the Low-E coating toward the interior of the building to protect it from hazing and premature wear.
In double-paned windows, the Low-E coating is typically applied to the sides of the glass that face each other in the air space so that it is protected from any exposure at all.
You may hear your glass supplier talk about soft-coat and hard-coat Low-E and be wondering which one you need. Soft-coat is usually more effective at blocking heat than hard-coat but it can only be used in double-paned applications. Hard-coat Low-E can be used in single-paned applications and is still very effective for all but the most southern climates. Even if you use a hard-coat Low-E in south Florida or Phoenix you will still enjoy the benefits of decreased heat transfer.
Is Low-E Glass Right For You?
Low-E has some definite benefits whether you live in a hot climate or a cold climate. It is used heavily in double-paned glass applications which if you’ve been a reader for long you know I am not a fan of due to their short lifespan and high failure rate. However, it can be used very effectively in single-paned form as well so that’s what I’ll be focusing on here today.
Low-E Storm Windows
I believe that in historic buildings there are two ways for Low-E glass to be used effectively. The most effective way to use Low-E glass in a historic window is by adding an exterior storm window with Low-E glass. You’ll need the hard-coat Low-E glass for this application and it can be very effective at upping the efficiency of your windows, often even beyond that of new replacement windows with double-paned Low-E!
You don’t necessarily need to build new storm windows. It is often just a matter of swapping out the existing glass with a Low-E substitute and for a very minor cost you have a big gain in efficiency. Easy improvement!
Low-E in Sash
If you don’t have storm windows or your windows won’t accommodate them like with historic steel windows then the next best option is to replace the glass in the windows themselves. I will preface this by saying that I am a huge fan of saving and preserving historic wavy glass. I don’t want it broken out or even swapped if possible, but if it’s a matter or trashing your windows or swapping the glass I see this option as a win because it saves historic windows.
You’ll want a hard-coat Low-E glass for this just like the storm windows and installing it is just a matter of digging out the old putty and glazing points and swapping the glass then re-glazing the window. Here’s a tutorial focused on replacing glass in steel windows.
Low-E Tint
The last option is probably the cheapest and easiest. Applying a tinted film to your window requires very little work and can be very effective (especially for the cost!). Finding a tint that blocks the heat and doesn’t block too much of the visible light is really the key. Gila makes a good and DIY friendly window film I have use before you can find here.
Make sure you apply your window film on the inside of the glass otherwise your tint will have a very short lifespan.
Remember, Low-E is not just for the summer, it is extremely effective at keeping heat in in the winter too so this is really an anytime of year project. Protect you furnishing from the fading effects of UV light and keep your house warmer in the winter and cooler in the summer, just keep those original historic windows and do it the smart way!
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I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.
Hi, thank you for your help. My question is: for single pane storm windows, will a hard coating low-e glass applied on the backside stay stable to the elements? We would prefer to have single pane low e glass for our storm windows instead of double pane low e glass (105 year old house). We have heard concerns that the coating might flake off with our harsh northern environment.
Hi, this may be an odd question but, I have looked everywhere and can’t find the info? My husband is making a project out of a commercial refrigerator that uses 2 low e thermal glass doors……..I can’t find any info on how much heat low e thermal glass can withstand???? Thanks!
Anderson custom storm door with low E full-view glass raised temperature to over 200 degrees The 30 yr old storm door i replaced was cooler with reg. glass This has damaged(cracked split ) my vintage 1936 interior door FYI
If a storm (window or door) is not vented properly it can really wreak havoc on things. I could be wrong but I would guess the door was sealed so tightly that it created a little oven inside. Low-E glass in and of itself could never cause this. There has to be some mitigating factors at play.
What would proper ventilation be?
There should be a minimal amount of venting and airflow allowing air into and out of the space between the doors. Either a few slits or holes at top and bottom or some other method to allow an air exchange.
We are planning on replacing about 7 sliders. 4 tripple and 3 double. Our (new to us) home is all about the view. Clarity is the very most important thing. Our contractor has recommended Milgard. Your opinion and suggestions please.
Are you a “Subject Matter Expert”?
I have low E factory tinted (privacy) dual pane windows. 1 pane is “tinted” & the other pane has the low E coating facing the inside air space of the window.
I live near Houston & the low E Factory tinted windows are on a West Wall.
My question is, “Which side should be installed to the inside?”
The factory tinted pane or the low E pane?
I cannot find anyone commenting about low E coatings and their effectiveness in the SHADE…. here in Arizona, we have SOME patio doors, for example that are shaded NEARLY all day…
Does a Low E coating on a single pane of glass do any good under these circumstances?
Signed,,,, frustrated lol
For those of you who commented that the costs are high, I believe one of the options is to NOT replace the actual windows (frame and glass,) but rather, call a glass shop, not a window shop and get an estimate about them swapping out the glass that is in your current window frames, NOT replacing the whole window (frame and glass) which can get very expensive very quick!
Sorry, I should have called it LOW e-glass that we have.
We hate our Pella e-glass and would never again go that route. We are elderly folks who need to hire a window washer, but NO ONE wants to handle that job. No squeegee—no workman, and I can’t blame them. The cloth skids and hangs up, the film on the window smears, etc.! I would now endure sun fading over this mess! Too bad we didn’t talk to some e-glass owners when we had the windows installed! Now we are stuck with windows no one wants to clean—including US. At age 79, we can’t handle the job.
Ugh, we are so sorry to hear that! Thank you for commenting on our blog and being part of The Craftsman Blog family. Thankfully, others can learn from your experience!
-Alyssa at The Craftsman Blog
Will low-e glass in a storm door protect the entry door (wood) from fading and the finish on it from cracking and peeling, the wood from warping, etc? Sun beats on the door through summer for a few hours each day. We have recently refinished the door and hope to protect it somehow from further damage. Thanks!
Low-e glass is usually not recommended on a storm door because it helps trap heat between the two doors, often ruining the entry door. In fact, most manufacturers do not even recommend ANY storm door in a very sunny entry.
Hello Scott, I just got a quote for Harvey Tru Channel storm windows and it’s going to eat up a huge part of my window budget. My question is, is getting the storms (with low e glass) going to be more effective that weatherstripping the old windows? I can’t do both, so which is more effective at getting rid of drafts and making the house more comfortable?
Get a quote from a company that sells glass, not windows. It will be very expensive to replace the actual window (fitted frame and glass) vs getting a glass company to take out the regular glass and put new low e glass in your old frames.
Scott, I just received a window estimate for new windows. I’m not happy that I don’t seem to have any choice but double pane and low-e. Are single pane windows still sold? Are any windows available without low-e glass? I want to have the thermal gain in winter and just close my thermal curtains / sheers in the summer during hot weather / sunny days. Would love to have storm windows for the winter, but do any window manufacturers offer such options?
Hello Dorothy,
My name is Alyssa and I work at The Craftsman Blog. I know this isn’t the *exact* answer to your question, but we have a directory of people who do what we do all over the country. Hopefully you can find someone in your area in our “network” and community and they can come take a look and give you a better answer upon seeing them than we fully can online. Thanks so much for your comment and best of luck to you! https://thecraftsmanblog.com/directory/
-Alyssa
Scott, what about solar gain in winter? I’m in northern New England and I follow the sun around our house on winter days. I’d hate to lose any of that free heat.
That’s definitely on of the downsides. For a hot climate it’s a no brainer, but in cold climates you lose the heat gain in the winter. So it depends on your situation if it will work well or not.