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Helpful? 2

High-Solar-Gain Glazing

Cold-climate glazing is surprisingly hard to find

Posted on Jul 31 2009 by Martin Holladay, GBA Advisor

Homeowners can now receive a federal tax credit for 30% of the cost of new energy-efficient windows. The credit was authorized by the American Recovery and Reinvestment Act (ARRA) signed by President Obama in February.

There’s just one problem with the new tax credit: the specifications for eligible windows were crafted by politicians, not window experts. The ARRA stipulates that eligible windows must have a maximum U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. of 0.30 and a maximum solar heat-gain coefficient (SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.) of 0.30 — requirements that have been dubbed “the 30-30 provision.”

Only low-solar-gain windows are eligible

There’s nothing wrong with the U-factor specification — except, perhaps, that it isn’t particularly stringent. The problematic provision is the SHGC spec.

By setting a maximum SHGC of 0.30, the ARRA actually excludes the best windows for cold climates. Cold-climate homes need windows with a SHGC in the range of 0.39 to 0.65; so if they comply with the tax-credit provisions, they’ll end up with windows that contribute to higher-than-necessary energy bills.

South-facing windows need a high SHGC

In Florida, solar heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss. from windows increases a home’s air conditioning load, so low-solar-gain windows are usually the best choice. Even in hot climates, however, high-solar-gain windows usually save energy during the winter.

Although some high-solar-gain windows — especially those facing east or west — can cause summer overheating, south-facing windows rarely cause overheating problems, especially if the windows are protected by a well designed roof overhang.

Since the average American family spends far more on space heating than on air conditioning, installing high-solar-gain windows on south walls makes sense for much of the country. Yet most U.S. window manufacturers have all but abandoned the market for high-solar-gain windows.

Low-solar-gain glazing is now the norm

During the 1980s, glazing manufacturers perfected spectrally selective coatings that made it possible to produce low-solar-gain insulated glazing. During the 1990s, as builders in hot climates learned how these coatings reduced cooling loads, low-solar-gain glazing took an increasing share of the U.S. market.

Most builders prefer to order just one type of glazing. Window manufacturers share the same interest, since they prefer to promote a limited number of glazing options. As a result, low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. insulated glazing with a low SHGC is fast becoming the industry norm, from the Canadian border to the Gulf of Mexico.

“Everyone is marketing windows for air-conditioning climates,” explained Andy Shapiro, an energy consultant in Montpelier, Vermont. The problem is exacerbated by the fact that the Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. program doesn’t recognize the benefits of high-solar-gain glazing. “Low-solar-gain windows will meet Energy Star guidelines all over the country, so that’s the glazing that all the window manufacturers have gone to,” Shapiro told me.

Industry laziness

According to Christopher Barry, Director of Technical Services at Pilkington Glass, the ascendancy of low-solar-gain glazing is partly due to rapid population growth in the U.S. Sunbelt. “The bulk of recent residential construction has been in the southern states, with low-solar-gain low-e glass,” said Barry. “Laziness on the part of designers and window manufacturers has ledLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. to forcing that one-size-fits-all glazing option on the whole market — north, central, and south — and sadly this is even beginning to happen in Canada.”

Soft-coat low-e glass — which tends to have a lower SHGC than hard-coat low-e — now accounts for most U.S. glazing. “They’re just selling soft-coat low-e,” says Ross DePaola, an engineer at Westlab, a Monona, Wisconsin, laboratory that performs NFRC testing for window manufacturers. “That hurts us in the winter time here in Wisconsin.”

Industry ignorance

Three years ago, when researching the availability of high-solar-gain glazing for an article in Energy Design Update, I quickly discovered that most U.S. window distributors don’t understand the advantages of high-solar-gain glazing.

Paul Kriescher, an energy consultant in Denver, agreed. “Window manufacturers don’t understand glazing,” Kriescher told me. “When you talk to the manufacturers’ sales representatives, they have no idea why you would want a high-solar-gain window on the south side of a house. It can be very frustrating. Sometimes they’ll say, ‘Well, we’ll have to research that.’ Then I have to tell them where they can get the glazing. It seems that the sales representatives have been given the mantra, ‘Go as low as possible with the solar heat-gain coefficient. Keep it simple.’ Windows represent one of the most profitable areas of building component manufacturing, but window manufacturers are not spending any time to educate their sales people on this issue. It’s a very big problem.”

More than one kind of low-e glazing

One of the few U.S. window representatives able to suggest high-solar-heat gain options was Jim Krahn, a technical expert at Marvin Windows. “We would recommend one of two products: LOF Energy Advantage from Pilkington, or Cardinal LoE-178,” said Krahn. (LoE-178 has subsequently been replaced by a new product, LoE-179.) He admitted, however, that Marvin doesn’t promote high-solar-gain glazing. “We offer it, but we don’t put many dollars behind promoting it,” admits Marvin Windows representative Jim Krahn. “We don’t get a request for high-solar-gain glazing very often.”

Jim Larsen, the director of technology marketing at Cardinal Glass, told me that LoE-178 has been around for years. “We introduced LoE-178 in 1982,” said Larsen. “Most of the window manufacturers offer it in their catalogs, but few people tend to stock it.” Cardinal’s LoE-179 #3 has a SHGC of 0.63; when installed in a typical window, it can result in a whole-window SHGC of 0.46.

High-solar-gain windows are so advantageous in northern climates that they make sense even for builders who can’t tell one orientation from another. “In Canada, even if windows are evenly distributed between the north and south, it’s still worth putting in high-solar-gain windows on all sides,” notes Morgan Hanam, manager for window services at Enermodal Engineering. “Our modeling using RESFEN proves it out, even considering the air-conditioning loads.” (RESFEN is a useful computer software program that evaluates the energy performance of residential windows to help designers optimize window specifications; it can be downloaded from the Web for free.)

Low-e doesn’t have to mean low SHGC

Stephen Thwaites, the technical director of Thermotech Fiberglass FenestrationTechnically, any transparent or translucent material plus any sash, frame, mullion, or divider attached to it, including windows, skylights, glass doors, and curtain walls., calculated that when Cardinal LoE2-170 glazing (low-solar-gain double glazing) is installed in a Thermotech frame, the whole-window SHGC is 0.28. The same window glazed with Pilkington Energy Advantage II (high-solar-gain double glazing) has a SHGC of 0.49. In other words, the window with high-solar-gain glazing admits 60% more solar heat than the low-solar-gain glazing. In spite of the significant difference in solar heat gain, the two windows have comparable U-factors (U-0.27 for the window with Cardinal LoE2-170, and U-0.30 for the window with Energy Advantage II).

Northern builders who settle for low-solar-gain glazing are “leaving a lot of BTUs on the table,” according to Thwaites. He compared the effect of double-pane Cardinal LoE2-170 with double-pane Pilkington Energy Advantage II; to simplify the comparison, Thwaites assumed that the same glazing was installed on all four orientations. For “a typical custom house with 200 square feet of windows” in a climate with a 212-day heating season, low-solar-gain windows result in the consumption of an additional 1,170 kWh (or 4 million BTUs) compared to high-solar-gain windows.

Paul Kriescher from Denver performed similar calculations. “For the home I’m in now — a production home where I specified the windows — assuming that natural gas costs 93 cents a therm, there is a net annual savings of $172 using windows with a SHGC of 0.55 on the south orientation instead of standard 0.32 SHGC windows,” Kriescher told me in 2006. “The modeling includes air-conditioning impacts.”

It’s available, until you try to buy it

Scott Pigg, a senior project manager at the Energy Center of Wisconsin, was so frustrated by the difficulties he encountered trying to buy high-solar-gain windows for his own home that he finally gave up.

“I had done a RESFEN analysis,” said Pigg. “I ran the simulations with hard-coat low-e and soft-coat low-e, and it made a big difference. We had decided to go with Marvin windows. When you call Marvin, they just ask, ‘Do you want a low-e coatingVery thin metallic coating on glass or plastic window glazing that reduces heat loss through the window; the coating emits less radiant energy (heat radiation), which makes it, in effect, reflective to that heat; boosts a window’s R-value and reduces its U-factor. ?’ That’s it for glazing options. I liked everything else about the Marvin windows, but I wanted a different low-e coating — I wanted a hard-coat low-e for better solar gain. I asked my contractor, and my contractor had no idea what I wanted. Then he came back to me, and said it would take three extra weeks. Then he said it couldn’t be done. I didn’t believe it, so I called Marvin directly. They said it was possible. Then my contractor said it would cost an extra $200 per window. I asked Marvin about that, and they wouldn’t give me any pricing information.”

Pigg ended up settling for low-solar-gain glazing, noting, “I will just have to suffer with windows that are somewhat better suited for southern cooling climates, as this seems to be where the entire industry is headed.”

Cold-climate builders should shop north of the border

Builders who have tried to buy high-solar-gain windows agree on one point: Most Canadian window manufacturers have a better understanding of high-solar-gain glazing than their U.S. counterparts. “All of the Canadian fiberglass window manufacturers get the concept of orientation-specific glazing,” said Andy Shapiro. “They are great.”

According to energy experts, the window manufacturers best able to handle requests for high-solar-gain glazing include Accurate Dorwin of Winnipeg, Manitoba; Fibertec Windows of Concord, Ontario; and Thermotech Fiberglass of Ottawa, Ontario.

Once you find the perfect windows, however, you’ll encounter one final frustration: the most energy-efficient windows aren’t eligible for the new tax credit. For reasons that remain unclear, the tax credit is reserved for windows that perform somewhat worse than those best suited for northern climates.

Last week’s blog: “Green Homes Don’t Have To Be Durable.”


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Image Credits:

  1. Bruce Richey

1.
Mon, 08/03/2009 - 09:28

High Solar Gain Glazing
by Donald Lintner

Helpful? -1

Martin,

I've been struggling with this option. We are using Serious 900 series windows and HSHG is an option but our house will face about 40 degrees west of south so our south windows really face SW and our east windows face SE. We'll have proper overhangs for south sun but it won't be totally effective due to the west angle. Our south windows are also partially shaded by a high ridge and a mix of conifer and deciduous trees on the south and west. This is in a 9500 degree day climate. The question came back from the window manufacturer asking if we REALLY wanted to specify any HSHG glass like that is a bad idea.


2.
Mon, 08/03/2009 - 12:53

A 9,500 degree day climate
by Martin Holladay, GBA Advisor

Helpful? 0

Donald,
A 9,500-degree-day climate is cold. I'm not sure where you are, but I imagine that you live somewhere where few people have air conditioning.

I would certainly choose high-solar-gain glazing for the SE orientation -- after all, mornings are probably cool, even in the summer. The SW orientation is more of a judgment call. It depends in part on whether you have a low glazing ratio or a huge expanse of glass -- as well as how your overhangs are designed.

Be sure to do a RESFEN analysis and examine your options. Remember, on sunny days from September to mid-May, you'll definitely appreciate the solar gain.


3.
Mon, 08/03/2009 - 20:01

Dual glazing
by Wayne Pendrey

Helpful? 0

This is very insightful for dual glazed windows, however they fall far short of triple glazing. Did you know that dual glazed windows are no longer legally sold in most of Europe. Pan-european building code has mandated triple glazing as part of passive design as the minimum to pass the building code.

Of course when you have energy cost such as they have in Europe, you are more motivated to stop wasting energy.

I have had many people try to tell me we do not need triple glazing here in Southern California, and I always reply...show me a zero energy cost for heating and cooling and then I will believe you, until then I agree with the Europeans and recommend that no one should settle for dual glazed windows, it doesn't cost that much more for another layer of glass and a second air space in between. And the additional soundproofing over dual-glazing is a huge additional benefit, reducing noise pollution substantially.

pushing for net energy homes...pendrey.consulting@gmail.com


4.
Tue, 08/04/2009 - 05:58

Different kinds of triple glazing
by Martin Holladay, GBA Advisor

Helpful? 0

Wayne,
You're right — many window buyers should be taking a serious look at triple glazing. Fortunately, the Canadian window manufacturers that I listed offer both low-SHGC and high-SHGC triple glazing. For example, Thermotech Fiberglass offers triple-glazed casement windows with whole-window SHGCs that range from a low of 0.25 up to a high of 0.47. Anyone living in a cold climate should choose a high-solar-gain window with triple glazing.

More information here:
http://www.thermotechfiberglass.com/case2.htm


5.
Wed, 08/05/2009 - 19:15

High SHGC Underrated
by Stephen Thwaites

Helpful? 0

A high SHGC is the underrated window characterisitic for northern housing. Here's an example to drive the point home.

Consider a north facing window in Toronto. (Toronto is warm by Canadian standards, but fairly typical for the Northern US). Whether it has a low or high SHGC glazing the north facing window is a net energy loser. However, it is more of a net energy loser if it has the better insulating low solar gain low-e, than if it has the poorer insulating high solar gain low-e. So even on the north where there is no direct sunshine, there is enough diffuse solar energy to play a very significant role in the energy balance of a window.

To be fair the difference between the two options for a north facing window is on the order of 1-2 kWh/ft^2 - so even if you heated with electricity, the difference in cost is on the order of $.10-.20/ft^2 of north facing window area over a northern house's 200 or so day heating season. Not alot of money.

Nevertheless the counterintuitive near parity of the two glazing options for a north facing window points to the underratedness of the SHGC.


6.
Thu, 08/06/2009 - 13:34

"underrated is an understatement"
by Rick

Helpful? -1

In the US, we are just far too spoiled and kingly to play around with passive solar. We all have (phoney) window shutters but haven't closed them at night for a century or so, and would be too lazy to close them now to get the best net btu out of south facing windows in the winter. Thermal mass is nothing but our fat American asses sitting around a fireplace.


7.
Thu, 08/06/2009 - 13:53

Thermal mass
by Martin Holladay, GBA Advisor

Helpful? 0

Rick,
Come now, you're being too harsh. The average U.S. home has other types of thermal mass — like a plasma TV, and granite countertops from Brazil, and all those empty soda cans in the recycling bin. It all adds up.


8.
Sat, 08/08/2009 - 13:36

30/30 window
by Anonymous

Helpful? -2

Blinds between the glass with low-e is a great fit it does both u factor with low-e hard coat clear glass on outside lite with the tilt and slide blinds great product check it out www.Royaltechwindows.com the windows are made in michigan and shipped across the country


9.
Tue, 09/22/2009 - 21:50

BSC Info Sheet
by Garth Sproule

Helpful? -2

I was just reviewing Building Science Corporation's "Information Sheet #001" titled "Residential Best Practices Criteria". Under the heading of windows, they recommend the following: For Climate Zones 1-3...max U value .40, max SHGC .35. For Climates Zones 4-8...max U value .35, max SHGC .40..

I would have hoped that these guys would have had no limit on SHGC's for northern zones...Any comment from anyone at BSC??


10.
Wed, 09/23/2009 - 03:57

BSC comment welcome
by Martin Holladay, GBA Advisor

Helpful? -1

Garth,
I have spoken to Joe Lstiburek on this issue. I would be happy for him to comment here directly. Although I hesitate to speak for him, I'll tell you what I remember. He worries that:
(1) The number of air-conditioned homes keeps increasing, and
(2) Production builders don't understand orientation, and need to be able to flip all of their home designs to any orientation in order to use these designs in large communities with lots that face any direction.

These concerns apply to many of Lstiburek's clients, but not to most GBA readers (I hope). Using high-solar-gain glazing requires thinking. For builders who can't think, it may be best to choose low-solar-gain glazing. You don't want to put massive amounts of high-solar-gain glazing on the west side of your house.


11.
Wed, 09/23/2009 - 09:00

AC concerns
by Garth Sproule

Helpful? -1

I can certainly understand Joe's concerns regarding AC. I live in southern Saskatchewan (9000 HDD) and even here, AC use is increasing. Most new homes are being built without regard to window orientation, but partly because most builders believe that low SHGC windows and AC will take care of any problems. I think that large areas of west facing glass of any SHGC and in any climate zone, result in an energy pig. The only solution regarding production builders would probably be code mandated...


12.
Mon, 10/19/2009 - 10:34

For people who don't use A/C,
by Neil Patel

Helpful? 0

For people who don't use A/C, and leave their window open the whole summer, low Solar Gain windows are really pointless.


14.
Tue, 11/10/2009 - 17:42

SHGC
by Rachel

Helpful? 0

My question is if higher SHGCs really matter on northern orientations - to the point of designing it into a home in a heating dominated climate? As Stephen Thwaites post would imply, they still gain from diffuse solar energy but it doesn't sound like much.


15.
Wed, 11/11/2009 - 07:27

It matters, but not much
by Martin Holladay, GBA Advisor

Helpful? 0

The amount of heat gained through northern windows during the winter is not great. Nevertheless, you might as well be harvesting heat instead of losing it. A low solar heat gain window will admit less heat and will often have a lower visible transmittance (be darker) -- something you don't want.

There is no danger of a north window leading to summer overheating, so the bottom line is: in a heating climate, be sure to select high solar heat gain windows for the north side of your house.


16.
Tue, 01/19/2010 - 01:31

Good points on low vs. high SGHC
by Anonymous

Helpful? -2

You’ve hit the nail on the head. It’s important to know what to expect and what is best for your area when thinking of buying windows.


17.
Sat, 02/06/2010 - 03:12

Wow
by jklingel

Helpful? 1

If heat-gaining windows are recommended for a 9,000 degree day area, I better find a company who will make some for me. Our dd is 14,000, and this could be important. I'm glad I found this site; I'm learning a lot and challenging pre-conceived ideas (like radiant floor heat in a super-insulated house.) Much to learn. j


18.
Sun, 02/28/2010 - 00:46

determining the degree day number
by Steph

Helpful? -1

How do you calculate the degree day number that I see used in many of these entries? Also, I'm a little confused. Should high SHGC windows be used only for south facing, only for north facing, or for both? What about east and west windows?


19.
Sun, 02/28/2010 - 07:01

Degree Days
by Martin Holladay, GBA Advisor

Helpful? 0

Steph,
Heating degree days are based on climate. They are usually listed by city; for example, ASHRAE Fundamentals has always maintained HDD information.

There are several Web sitest that include HDD information, including
http://www.degreedays.net/
http://www.huduser.org/portal/resources/UtilityModel/hdd.html

"SHGC" is an acronym that stands for "solar heat gain coefficient." It can be caluclated for any type of glazing. Some windows have a high SHGC, some have a low SHGC -- but every window has a SHGC.

The best SHGC for a home's windows depends on climate, orientation, and whether or not the windows have summer shading. There is no single answer to your SHGC question.


20.
Tue, 03/02/2010 - 02:35

a replacement window consumer looking for answers
by Steph

Helpful? 0

Thanks for your reply. I apologize because I am very much a novice at all this, but we have a house full of windows that are going to need to be replaced over the next few years and I would like to make an educated decision before investing a bundle. I have been reading as much as I can and ran across your website this weekend. Up until then, I had believed that the recommendations based on the government tax credit were what I should follow. Now I'm second guessing it all. The trouble is that I'm not an expert. How does an average consumer figure out what are the best windows for their particular house? Are there consultants that I should be able to locate? Where do I begin? I did review the sites you recommended for degree days and, if I understand correctly, the location of my house has 7200 heating degree days and 1100 cooling degree days. I live in Boise, ID. Almost all of my windows face the south and we do have a large overhang.

Is it true that the low-E glazing reflects summer sun and lets in the heat of the lower winter sun? That is what one of the Marvin brochures indicated. But if the window has a low SHGC, then doesn't that mean that the glazing does not even allow much of the winter solar gain?

Thanks again for your help.


21.
Tue, 03/02/2010 - 07:14

Low-e glazing
by Martin Holladay, GBA Advisor

Helpful? 0

Steph,
No, it is not true that "low-e glazing reflects summer sun and lets in the heat of the lower winter sun."

The effect of a low-e coating is to lower a window's U-factor. That's good. However, knowing a window's U-factor tells you nothing about its SHGC. You can have a low-e window with a low SHGC, and you can also have a low-e window with a high SHGC.

If you want a window that doesn't admit solar heat, choose a window with a low SHGC. If you want a window that admits solar heat, choose a window with a high SHGC. There is no such thing as a window with a variable SHGC (except for a few experimental windows that use an electrical current to vary the window's tint — windows that aren't sold for residential use). A window can't tell the difference between the winter sun and the summer sun.

You can limit summer overheating on the south side of your house by adjusting the roof overhang so that the windows are shaded during the hottest time of the summer and unshaded in the middle of winter.

In Boise, Idaho, you probably want windows with a high SHGC on the south side of your house. The only exception would be a house with a very large amount of south glazing that suffers from summer overheating.


22.
Thu, 03/04/2010 - 15:04

manufacturers
by Richard

Helpful? 0

This is a great site. Thanks to all who post here. I'm in Baltimore, with 4500 heating degree days and 1100 cooling degree days. I'm planning an addition that will have many south-facing windows. I'm thinking I should seek out high SHGC with low-E to maximize passive wintertime solar heat. Would you agree this this? I see that Cardinal lowE2-179 and Guardian ClimaGuard make the glass, but I can't find a manufacturer who puts it into an all-fiberglass window. Anyone know of a well-built window with this glass? Maybe I need to look to Canadian window manufacturers?


23.
Fri, 03/05/2010 - 04:42

Fiberglass windows with high SHGC glazing
by Martin Holladay, GBA Advisor

Helpful? 1

Richard,
If you want a fiberglass window with high SHGC glazing — look north. There are several good Canadian window manufacturers to choose from, including Thermotech, Inline, Fibertec, Accurate Dorwin, or Duxton.


24.
Mon, 03/08/2010 - 18:01

Thank you, Martin. I will
by Richard

Helpful? 0

Thank you, Martin. I will look into them. I knew of Thermotech already, but would like to see if the others might make single- or double-hung windows.


25.
Thu, 03/11/2010 - 01:36

R-value
by Steph

Helpful? 1

I've started talking to Serious Windows and Thermotech. I've started to see R-value numbers floating around. What does that refer to?


26.
Thu, 03/11/2010 - 05:12

R-values
by Martin Holladay, GBA Advisor

Helpful? 0

Steph,
A window's R-value is the inverse of its U-factor. In other words, R=1/U and U=1/R.


27.
Wed, 03/17/2010 - 17:46

SHGC + VT
by rita addison

Helpful? -2

When I visited NESEA last week I made sure to leave our building plans with Accurate Dorwin, Inline, Armaclad (which I later regretted since I've researched heat mirrors) and Marvin Integrity.
Everything I've read here and other research indicates that if I want an SHGC of .4 and VT of at least .79 I should try to get LoE 179 (Cardinal). We are building a passive solar house, so I want these specs for the southern windows and will settle for NFSC 3, 3 elsewhere.
I just heard back from Marvin Integrity and they said LoE 179 was not an option. LoE in the 200 and 300 was available, with abysmal visible transmission.
I refuse to live with dark windows!
If I remember correctly, Dorwin also has a low VT.
What else can I do? We start building in 3 weeks. Please, your advice.


28.
Thu, 03/18/2010 - 05:36

High VT windows
by Martin Holladay, GBA Advisor

Helpful? 0

Vita,
You set a high bar for VT — which is OK, it's your house. If you're aiming for a VT of 0.79, I think your only choice is clear double glazing (with no low-e coatings or argon). That is an available option from many window manufacturers. According to the Thermotech Web site (www.thermotechfiberglass.com), their casement windows with clear double glazing have a U-factor of 0.42.

That's a pretty lousy U-factor, of course, but it will give you the very high VT (glazing-only VT of 0.81) you are seeking.

If you want a much better U-factor -- for example, a whole-window U-factor of 0.23 -- you could choose LOF EA2 glazing. But then your glazing-only VT drops to 0.68.

Your list of manufacturers could be expanded. Try Thermotech (www.thermotechfiberglass.com), Duxton Windows, and Fibertec as well as the ones you listed.


29.
Wed, 08/18/2010 - 21:32

Window Comparison
by Russ Hellem

Helpful? 0

We have struggled to find relevant information to compare energy efficient windows. We finally went through the exercise to put all of the information in one place. You can find our window comparison spreadsheet with performance info and pricing on our website. http://energetechs.com/resources/window-comparison-spreadsheet/

Feel free to comment or send us information on any other windows you have data on.


30.
Thu, 08/19/2010 - 05:17

Response to Russ
by Martin Holladay, GBA Advisor

Helpful? 0

Russ,
My response is the same as the last time you posted this link on a different GBA page:

As far as I can tell, you forgot to answer an important question: are these whole-window specifications (including the frame) or glazing-only specifications? As you probably know, European manufacturers usually provide glazing-only specifications (especially for SHGC), while US manufacturers usually provide whole-window specifications (as required by the NFRC).

Without a clear statement on this question, it's hard to know whether the spreadsheet is useful.


31.
Sat, 12/11/2010 - 17:56

Low-E 179
by Gib

Helpful? 1

Your article recommends Low-E 178 as one option for High SHGC. The Marvin website offers Low-E 179 again for high SHGC. Is their a substantial difference?


32.
Sun, 12/12/2010 - 07:38

Edited Sun, 12/12/2010 - 07:40.

Response to Gib
by Martin Holladay, GBA Advisor

Helpful? -2

Gib,
Cardinal has introduced Lo-E 179 as a replacement for Lo-E 178. It's just as good as, or better than, the product it replaces.

Thanks for your post. I will correct the text of the article.


33.
Wed, 08/31/2011 - 23:36

Window tuning for northern climes
by Kristi Appelhans

Helpful? -1

Excellent article outlining all the reasons for properly tuning windows according to climate rather than convention, and good resources to boot. I have been advocating for 5 years that we consider window orientation and evergreen and deciduous tree cover to optimize solar heat gain in our heating-dominated climate - with only limited success in part due to the difficulty of finding even semi-convenient sources for glazing. Many folks just don't want to mess with it regardless of the economic or sustainability consequences. More articles like this one may begin to educate enough people to actually see the trend shift towards thoughtful window tuning.


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