Image Credit: Photo: Bronwyn Barry, Assoc. AIA
Image Credit: Photo: Bronwyn Barry, Assoc. AIA The Edelglass residence in Vermont uses Loewen aluminum-clad double- and triple-glazed windows. Window design and selection was optimized for budget, durability, good insulation value, and passive-solar heat gain on the southern exposure.
Image Credit: Photo: Kirstin Edelglass
More Energy Solutions
It has been a great spring so far for spotting wildlife. A neighbor told me he was shooing a black bear away from his garbage the other day when he saw that he had also frightened off a moose that was also in the neighborhood. Perhaps the moose and bear are rehearsing for a new wildlife buddy movie?
I spotted a porcupine crossing the driveway last week. I love that fact that porcupines don’t seem to give a damn. I’m sure that they are capable of running, but unlike a lot of animals that run when encountered, porcupines seem to just keep on going wherever they were going, at the same measured pace, with the same loopy sort of lope. When worse comes to worst, they can simply sit there, knowing that only a handful of predators can get around those quills.
What’s the highest-tech part of your home?
What’s the highest-tech piece of engineering that’s a part of your home or workplace? I would suggest that by some measure, it’s not your furnace, your fridge, your dishwasher, your hot water heater, or even your ground-source heat pump and radiant heat, if you have that. It’s your windows.
Look at what we ask windows to do. We want a visual connection to the outdoors that lets in daylight and that is itself pleasant to look at, both from the inside and the outside. We expect windows to provide fresh air and cooling breezes at times, but at other times we expect them to be completely airtight and provide good thermal insulation. Insects should be kept out; children and pets in. In heating climates, we want to get solar heat gain from windows, but not too much, and in all climates we don’t want glare.
We also need windows to be durable in every way: resistant to condensation, wind, driving rain and ice, as well as the occasional baseball from over the neighbor’s fence or hurricane-driven debris. Windows must operate easily and accommodate attachments like curtains, awnings, and other devices. We want windows that are quick to install, that integrate with the rest of the building envelope, and that won’t break the bank. Given that they are a big investment, they should last a long time — several decades at least. We want windows to not cause undue environmental harm during their life cycle, whether from material extraction, manufacture, disposal, or as a hazard to birds.
Windows do it all
And like the porcupine, windows do all that by just sitting there — very few, simple “moving parts,” no motors, no pumps, no electricity. How is this possible? The secret is in the engineering. The last 20 years have brought us a whole new generation of high-performance windows that your grandparents wouldn’t recognize — double-glazed with low-emissivity (low-e) coatings. Today we are in a midst of the birth of a new generation of windows. Many are now triple-glazed, incorporate multiple low-e coatings, improved frame insulation, and more.
It’ll take a couple columns to unpack everything about windows that’s worth talking about, so consider this a starter. (If you want to cut to the chase, read my full guide to window selection in Environmental Building News.) In most cases, energy performance will determine the environmental impact of windows over their lifetime, and with most current windows on the market, that will be determined by glazing choices.
The number of glazing choices out there can be dizzying. But pay attention and do your homework. It could be easy to get talked into choosing windows that sound really good, but that don’t make sense for your climate, your building, or even for the specific wall where you install them.
Doubling down on glazing
With storm windows dating back 200 years and sealed double-glazing units dating to the 1930s, adding a second layer of glazing has long been the first step for window manufacturers toward improving energy performance. A second layer of glazing — or a third in the case of triple-glazed windows — improves window insulation by trapping dead air. For example, going from one layer of glass to two with a ¼” (6 mm) air space increases the center-of-glass insulating value from R-0.9 to R-1.75.
Double-glazing might have sounded good 10 years ago, but triple-glazing is now becoming more common in both residential and commercial windows. Triple-glazing is provided through a third layer — either a third pane of glass between the two outside panes or, less commonly, a plastic film suspended between the two panes of glass (Heat Mirror is the best-known film product).
Because heat conduction across the air space in a sealed insulated glass unit (IGU) contributes to heat loss, we can improve performance by replacing the air with a lower-conductivity gas. The most commonly used gas fill is 90% argon, which is plentiful, inexpensive, and inert. With low-e glass in an IGU with ½” (13 mm) spacing, argon boosts the center-of-glass insulating value from U-0.29 to U-0.23 (R-3.45 to R-4.35). More expensive gases like krypton perform even better and can be found in the highest-performing windows or where a thinner profile is desired. Getting argon is a no-brainer, but if it’s not specified, you probably aren’t getting it — again, ask.
Do argon and krypton leak over time?
You might think — why invest in argon or krypton, when those gases could leak from the window over time? As a technical bulletin from Cardinal Glass states, “No organic seal ultimately can prevent the internal atmosphere of an IGU from becoming the same as the ambient atmosphere over time.” Since the “ambient atmosphere” we breathe contains just 1% argon and much more nitrogen and other gases, that argon or krypton will eventually escape. Accelerated-weathering tests used by major manufacturers require 80% argon to remain after testing; this suggests that after years of service, most of the argon will remain. Citing German research, Robert Clarke of Serious Energy (formerly Alpen Windows) told me that a loss of 1% of the gas per year is expected. While the benefits of gas fills may not be permanent, they are substantial and long-lasting, and the incremental price premium is easily justified.
A third generation of low-e coatings
The most common type of low-e coating is called soft, or sputtered, coat. Thin layers of silver and anti-reflective coatings are applied to the glass surface through a vacuum deposition process. Because the coating is delicate, it must be protected within the IGU.
Pyrolytic or hard-coat low-e glazings have a thin layer of tin oxide incorporated into the surface of the glass during manufacture when the glass is still hot. Hard-coat low-e glazings are durable and can be used in single-glazed windows or storm panels, but their emissivity is not as low as that of soft-coat low-e glazings. Hard-coat glazings generally offer weaker insulating value compared with soft-coat glazings but have higher solar-heat-gain values.
Low-e technology has changed tremendously since single low-e coatings first became common in the 1980s. In the 1990s, a double (layered) low-e coating came along, dubbed “low-e2” or “low-e squared.” According to Clarke, the evolution was due to a market demand for cooler glass, with lower solar-heat-gain. Particularly given that demand, the market also shifted to favor soft coats. Adding standard soft-coat low-e2 glazing to an IGU with a ½” air space increases the center-of-glass insulating value from U-0.49 to U-0.29 (R-2.04 to R-3.45).
The 2000s have seen “low-e3” (or “low-e cubed”) glazing take hold, with yet another layered low-e coating. Clarke told EBN that again a demand for reduced heat gain, particularly for cooling-dominated office buildings, has driven this shift, along with technical advances allowing coatings that cut out the low and high infrared light while leaving more of the visible light to pass through. Today, low-e, low-e2, and low-e3 coatings are all available, with single low-e coatings making a comeback for heating-dominated climates, and improved hard coatings also available for applications favoring solar heat gain.
Asking your dealer or builder what type of low-e coating you’re getting, and what attributes it offers, is essential. If you’re a builder, think carefully about what you’re providing to your client — the choice will matter for decades to come.
We’ll add more pieces to the window performance puzzle — and begin to put those pieces together — in future columns. Keep your questions, comments, and wildlife stories coming!
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22 Comments
pricing window options
I got the following comment via email in response to this column. I'd be interested in hearing if anyone has input on this issue (window pricing):
Construction has just begun on a small sunroom addition to my home. The problem with getting great windows is not product availability, but the awkward way they are sold.
Building supply dealers seldom post prices of anything. Items which are ordered, like windows that have lots of options and sizes, are much worse – requiring the entry of data into a computer to get a quote. The quote of course is for the whole window, making it really tedious to test out individual options (I had them do that for hi-transparency window screens vs. the standard mesh, but it would be nuts to run that for Pine vs. Doug Fir, solid brass vs. anodized hardware, krypton vs. argon vs. air, etc.). The retail staff, though both knowledgeable and helpful, cannot possibly keep prices for all those options in their heads, and are probably reluctant to make guesses. (Nothing good can come from a customer mistaking a ballpark guess for a quote.)
Net result: it is ridiculously difficult to get a cost comparison of option A vs. option B, on anything. In my case of a south-facing sun room where I knew I’d be starting a lot of veggie seedlings in spring, I depended on my own reading and research in preferring clear glass (full-spectrum, high solar gain), and triple pane (reduced heat loss). This unusual combination was of course not in the computer, and although Marvin really does make each window in response to customer orders, and has no trouble making triple-pane clear windows, it took several DAYS to get a price on it. Going through that process for the dozens of decisions in a given project is simply not going to happen. Even a highly motivated customer has little choice but to just give up and trust the contractor to do something reasonable. And still miss here and there. Your note that using argon gas was a no-brainer came too late, and I didn’t expend the effort to price argon vs. air.
The other problem is that while it is easy to find a competent architect or contractor, finding one with that extra zeal for energy efficiency is another matter altogether. Neither my architect nor any of the three highly regarded contractors showed any special spark in this area.
Does anyone have feedback on effective ways to price out high-performance window options? Is this only a problem with one-off projects -- does the difficulty go away when working at some volume?
Response to Unnamed Window Shopper
Dear Unnamed Window Shopper,
You are 100% correct. I couldn't agree with you more. The window industry needs to make pricing much more transparent. It's time for the window industry to enter the 21st century, and to realize the price transparency will make their business stronger, not weaker.
Just as "no haggling" car sales lots attract customers who are sick and tired of buying a car from a dealer whose prices are suspect and ever-changing, a window manufacturer that posted prices online would immediately gain customers who would be grateful for the transparency.
Window Shopper
Man, you hit the nail on the head. I don't have the time -- nor, I might add -- the credibility to get the attention I'd need for accurate pricing.
I'll tell you what I've done --
First, finding a contractor -- we have several HERS raters in the area, and there are a couple of builders (couple = 2) who advertise their work as energy-efficient or EnergyStar or EarthCraft or whatever. So I talked to the HERS raters for recommendations and the builders to see if we were in the same chapter. From there, I've picked two.
Then, finding prices. I'm not ready to build, but I am ready to figure out what I may actually be able to afford from the options I like. So I prepared a list of options for foundation, wall (incl windows), and roof, then I hired two of the HERS dudes to prepare prices (installed by local help, not only materials) based on what they thought was going to fit the local talent pool, code enforcers, and so on.
It was remarkable how close the bids were in most respects.
Just as an addon to the blog -- M-W windows was bought out by a group called PlyGem a couple of years ago; their windows are promoted by the building yards ... and they have a new Triple-Pane window they call the R-5! Yes, it's a US window but I don't know if it's in production yet and don't have specs.
Joe
window glass performance
As a bit of follow up on glass / LowE performance…
LowE coatings are specifically designed to improve window energy performance by inhibiting the transference of heat thru the glass.
Two versions
- hardcoat or pyrolitic
- softcoat or sputter
Three types
- High Solar Heat Gain (pyrolitic or single silver sputter)
- Moderate Solar Heat Gain (special coated pyrolitic or dual silver sputter)
- Low Solar Heat Gain (triple silver sputter)
For comparison of common LoE (Cardinal) coating performance numbers - inside to outside heat transfer (losses) thru window glass in Btu/hr/ft² at a winter time ΔT of 70° - borrowed directly from the Cardinal Glass Industries Residential Glass Guide (and I am so not sure this is going to work when I post it...).
------------------- Radiant - Conductive - Total Btu’s - SHGC - CoG U-Value
Dual pane clear - 21 - 13 - 34 - .78 - .48
Dual pane LoE 179* (single silver) - 5 - 15 - 20 - .70 - .28
Dual pane LoE² 272 (dual silver) - 2 - 16 - 18 - .41 - .25
Dual pane LoE³ 366 (triple silver) - 1 - 16 - 17 - .27 - .24
Triple pane LoE 179* (single silver) - 2 - 11 - 13 - . 57 - .14
Triple pane LoE² 272 (dual silver) - 1 - 11 - 12 - .35 - .13
Triple pane LoE³ 366 (triple silver) - 1 - 10 - 11 - .24 - .12
*LoE-179 is currently being phased out in favor of the newer LoE-180.
LoE-180 has a SHGC of .69 versus LoE-179’s SHGC of .70 (in a dual pane using 3mm or 1/8” glass), but an improved U-value of .26 for LoE-180 versus .28 for LoE- 179.
U-value based on ½” airspace and argon fill.
Notice that while the LoE coatings cut down on radiant heat loss, conductive loss actually increases slightly but the increase is more than offset by the improvement in radiant loss.
As a quick (and reasonably accurate) rule-of-thumb for calculating R or U value performance in a window system:
Single Pane – R1 or U1
Single Pane and storm window – R2 or U.5
Dual Pane, clear glass – R2 or U.5
Dual Pane, LowE coated – R3 or U.33
Dual Pane, LowE coated, Argon fill – R-3.5 or U.29
Triple Pane or dual pane with storm, all clear glass – R3 or U.33
Triple Pane, one lite LowE coated – R4 or U.25
Triple Pane, two lites LowE coated – R5 or U.20
Triple Pane, two lites LowE coated, argon fill – R6 or U.17
Triple Pane, two lites LowE coated, krypton fill – R7 or U.14
Keeping in mind of course that these numbers will vary somewhat depending on factors such as airspace width, type of LowE coating used, sash and frame materials, window style, and other specific window construction details.
Window price options
I understand and agree with many of the points in this but I would also point out a couple things.
1) As a consumer, you really should have SOME idea of what you would like from you windows. Walking into a building center and asking the associate to option everything is not ok. Oak vs. cedar, sure, but do you really need to know how much more it is for roll up screens if you already know your budget is tight?
2) I think one of the biggest factors people fail to consider is the huge cost associated with manufacturering windows and doors. Think about the amount of inventory required. A manufacturer is trying to manage the movement of product on a production schedule and there is no such thing as a regular schedule for a contractor.
To answer your question, "Does anyone have feedback on effective ways to price out high-performance window options?", yes. Sit down with a trusted window supplier and discuss the goals of the project before even unrolling the plans. Your supplier should have a canvas in their mind and as you talk they should be mentally selecting the right options for you. For instance, if you're going to build a "passive solar" home they darn well better not be looking at LoE 366 or LoE 240. LoE 180 should immidiatly come to their mind (assuming they use Cardinal glass). If you require a window with a u-value of let's say .25, tell your window person that ASAP. There are a lot of window options today but getting pricing on all of them is a waste of everyone's time. Think of it this way, if the average good quality wood/clad window is $500 and the most expensive up-grade available is 30% more, how many ways does your window person really need to formally bid the project? Get a good idea of what product will best suit your needs and THEN ask for the bid. Blindly dropping plans into a window person's hand and having them bid it anyway they chose is dangerous.
Response to Tom Green
Tom,
Your vision of the helpful window rep is inspiring but somewhat naive.
"For instance, if you're going to build a passive solar home they darn well better not be looking at LoE 366 or LoE 240." If only such window reps were common! I've spoken to dozens of them over the years, and the vast majority of window reps have never heard of high solar gain glazing.
If you want to request it, first you have to explain it to them. Then, a week later, you'll get a price -- for windows with low-solar gain glazing, because the rep doesn't know the difference between "solar control" and "high solar gain."
LoE i81
We're lucky in Maine to have some very good window reps who know how the windows are made, and the different glass options.
Have you checked out this glass yet? http://www.cardinalcorp.com/products/coated-glass/loe-i81-glass/
It's probably not been NFRC tested in most windows yet, so you may not see it advertised, but it gets you low U factors and high SHGCs.
(and no, I don't work for Cardinal.... or any window/glass company)
Whining much?
"This unusual combination was of course not in the computer, and although Marvin really does make each window in response to customer orders, and has no trouble making triple-pane clear windows, it took several DAYS to get a price on it"
OK, let me see if I got this right. The un-named complainer has a spec which is unusual and (it appears) not fully considered. The project is small and the complainer is
a) unlikely to be a repeat customer
b) probably getting bids from other suppliers on the same job, quite possibly based on different specs
c) will probably take a month to confirm the order (if at all,) and
d) nevertheless seems to expect instant gratification in customer service
That the supplier ONLY took a couple of days to turn this around (how busy were they with other, perhaps more reliable customers?) is pretty remarkable. I have a number of complaints about the US window industry, but given the constantly evolving and complex nature of their business, failing to get a trustworthy bid out in less than two days in such conditions would not be one of them.
Perspective from a Green Products Dealer
At Green with Envy Home Store, we deal with many different types of questions and customers. Just as I was writing this comment, a customer entered the store and started asking questions about Carpets. What percent is Jute compared to another product, what makes it biodegradable and Can we sew the carpet? I knew most of the answers but sometimes we do not know the answers to tough questions like the ones listed in the original post. The solution is really simple: Just simply find out the answers and forward them in a timely manner to the customer. In my opinion, the options for products, especially windows, has become overwhelming and we just cannot keep up with the changes. Most Sales Reps cannot keep up either!! I always think about when I am purchasing products for my business and home. I research and ask questions to the sales rep. How do I know if my question is hard or uncommon?
responses
James, I don't think the customer is whining about the windows supplier, who you defend ably. I think they're calling out the window supply system as a whole. I would also defend any whining that they may or may not do by saying that they sent me this account as a personal aside, and weren't expecting it to be dissected on a forum like this. I posted it to get feedback from others who have been in this situation, and the response has been great.
Thanks to James, Martin, Greg, and others for insightful comments.
windows for a new build in Colorado
Thanks for this article, and the comments. Our house in the mountains of Colorado burnt in a forest fire and we are building a energy-efficient (almost passivehaus standard) house. I have read many of the green building articles on low e, high solar gain, fiberglass windows - and have found it almost impossible to find/price windows. Each window company has a different way of presenting numbers...any suggestions for brands?
Response to Joe on R-5 and Martin on SHGC
Joe,
We recently found the Volume Window Purchase program was out there with an option to price out affordable, efficient windows. Fixed windows are required to have a u-value of .20 while operable windows have to meet .22 or better. The "volume" requirements are that you must buy 20 windows to get the reduced pricing. We did some research but unfortunately one of our main requirements (German style Tilt and Turn mechanisms) were not available so we looked elsewhere. This is a government sponsored program and the web link is http://www.windowsvolumepurchase.org/ There is some information on the web about buying smaller quantities but it is only offered by a few vendors.
Martin - your comment on the window reps not knowing about solar heat gain ihit the mark, almost. We are building a Passive House in NC and wanted good u-values, high SHGC, and good VT (not to mention low air leakage). Our initial quest was with US companies but nothing met our requirements (and reps typically weren't very knowledgable on the options available) so we turned to European (German and Lithuanian) and Canadian manufacturers who for the most part fully understood the need for SHGC as part of the design criteria. I suspect part of that is that we were dealing with companies who dealt regularly with passive house requirements.
We did see a wide range of knowledge by the salesmen of their product lines and settled on a German PVC window with a Ut of .16 (Ucog .11), VT of .52 and SHGC of about .50 - and very importantly they offered our Tilt and turn option. The rep we have been working with is very knowledgable and he's in constant contact with the engineer in Germany to ensure we don't run into problems down the line. Granted these windows aren't the $125 specials found in the Sunday paper or mailer coupons but they also aren't the same quality. For the record, these are triple-pane, argon filled with a warm-edge spacer with 4/14/4/14/4 glass/argon/glass/argon/glass construction.
What about Skylights? We have recently been trying to find NFRC rated skylights but our quest is still ongoing. We managed to discover one manufacturer claiming R-20 from a tubular skylight but we haven't been able to get any certification data - the claim is backed by a professional engineer's statement on his calculations of the performance (without any testing). We have also seen nanogel products that can be retrofitted with an advertised gain of R-9 (the unit installs in the skylight shaft). Are there any other solutions out there for highly efficient skylights?
Orianne, our blog is at http://pittsboropassivhaus.blogspot.com and in today's post I listed the window manufacturer we selected (with the rep here in NC). Word of caution to all is that we're not the experts but we're learning a lot as we move toward construction.
Response to John Clarke
John,
It's OK to mention brand names at the GBA site. If I read your blog correctly, you have decided to buy Hoco windows. I found this manufacturer's site:
http://alt.hocoplast.com/hp653/Wood-aluminium-windows.htm
Is that the company?
Response to Martin
Martin,
Yes - we're using Hoco 150 profile windows and different profiles for doors. The one exception is "fire rated" door between the garage and house which we are still in search of.
The other piece of this that we're exploring is the expanding foam tape system that appears widely used in Germany. Wurth is one name that we've seen but there are others. One of the tape mounting/sealing systems even has two separate types of tape; air/water open for the outside seal and closed for the inside seal. The theory there is that any moisture that does get into the space around the frame will be able to exfiltrate from the outside and prevent mold/rot from growing. The one version of expanding foam tape we saw expanded in minutes to hours depending on temperature and then over a period of a day or so hardened into a closed-cell seal. Henselstone's (that high end Gayko window) claim is that you can almost do without the through-frame screws because the tape is so strong.
More questions for John Clarke
John,
Are you importing the Hoco windows from Germany, or is there a North American importer and distributor?
HOCO Windows
Martin,
We're working with an importer here in North Carolina who is dealing directly with the manufacturer in Germany. Because these are made-to-order windows we have been in a continuous dialogue to make sure the options we want are included and the sizes/configuration are correct. The rep has called us with areas he wanted to bring to our attention so we didn't get the windows and have the "oh, that won't work" reaction. So far it's been quite a good experience.
Distributor for Hoco
John,
I've been assembling a list of distributors and importers of European Passivhaus windows, so I'd love to know the name of the importer you are dealing with.
Hoco Distributor
Martin,
I'll get that info and post it here for you - I have to dig through the piles of paper to find it! I'll get the information for the other companies as well though I suspect you may already have them.
Passive House Window Sources
Martin,
Here are the European distributors/reps we've been in contact with. We focused on their vinyl windows but all offered upgrades and PH Certified windows but we opted for qualifying due to the cost differential. My wife is much more organized than I am and made this list in short order.
Hoco
Armin Reischl
Product Manager
Eurostar Fenestration LLC
Phone: (704) 907-7397
Henselstone Window and Door Systems, Inc.
113 Henselstone Lane
P.O. Box 116
Amissville, Virginia 20106
Phone: (540) 937-5796
Fax: (540) 937-3383
e-mail: info(at)henselstone.com
Forrest Thornton Deleot
Henselstone Window and Door Systems
905 Godber Street
Charleston, SC 29412
phone: (843) 408-9653
fax: (803) 753-0073
Aurimas Sabulis
Intus Windows
1042 Wisconsin Avenue, NW
2nd Floor
Washington DC, 20007
202-701-3208
[email protected]
http://www.intuswindows.com
Kjell Hatlehol
ENERGATE-US
H Window Company, LLC
401 17th Ave. W.
Ashland, WI 54806
Phone: 715-685-2793
Fax: 715-685-9441
[email protected]
http://www.energate.us
[email protected]
http://www.hwindow.com
Storms and Quilts
All the high-tech window technology begs the question: Are low-tech measures like good storm windows or interior night-time insulation like window quilts as effective as the latest triple glazed from Germany? Wouldn't a good, sealed storm window, by covering the frames, eliminate the leaking most associated with double hungs? And wouldn't night-time drapes avoid the need for infrared-blocking coatings? Or would any added performance of storms and quilts not justify the cost of the new super windows?
window attachments
Michael, these are excellent questions, and ones that I'll be writing about in future posts. In the meantime, I recommend an article from EBN, Making Windows Work Better, which discusses brand-new research on the effectiveness of these features:
ThermaTru Marketing Tactics
In response to my question about Low E insulating glass in its Benchmark French doors, ThermaTru responded that "argon gas will dissipate over time." A call to customer service would not and could not back that up. fYI, the article above about cites one per cent a year as possible dissipation. conclusion? Be wary of ThermaTru marketing jargon that they won't back up with fact. (see below.)
Good morning,
Thank you for considering Benchmark by Therma-Tru. In response to your email our glass is clear insulated. It is not argon filled. Please be aware that argon gas will dissipate over time.
Should you need additional information or assistance, please email customer service or feel free to call us at (866) 584-3668.
Sincerely,
Customer Support
Tru-Logistics Inc.
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