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A Lesson On Windows - This Is Instructive!

Here is everything you need to know about efficient windows.  When you buy a new house, or replace your windows, you want to know about two things -

1.  Do they have high, moderate or low solar gain, and,

2.  What is the U-factor?  From this you can calculate the U-value.

New, efficient windows are designed for different climates.  In a cold climate you probably would want high solar gain.  In hot and sunny places, obviously, low solar gain would be preferable.  High solar gain transmits about 71% of solar heat to the interior, yet protect heat from escaping the house.  Low solar gain offer only about 27% solar-heat transmission.  (For moderate solar gain windows it would be about 39%, by comparison.)

How do they do this?

With low-E coatings.  Short for low emittance, low-E coatings are microscopically-thin layers of metal or metal oxide, virtually invisible to gain a good U-factor and reduce heat flow. They let in as much as 75% of visible light.

The U-factor is very similar to the R-value of insulation.  The lower the number, the higher the insulative value.  For example, a triple-pane window would have a U-factor of .15.  Divide this number into 1 to get the U-value, or the equivalent of an R-value of 6.67.  Excellent!  (Your walls are probably R-13.)

That is why when you put your hand on the interior pane of an efficient window bathing in hot sunlight, the pane feels cool.  That is a good judge of an efficient window.

This low-E coating may be invisible to our eyes, but not if you pass light through it.  Lookie here!

I took this photo in a new home the other day in bustling Boyce VA.  This clearly demonstrates the "invisible" coatings on these windows.  These are good windows!

The lower part of the photo is where light is passing through no glass.  The upper part it is passing through one window and the middle through two windows.  Remember, each window is made up of two panes of glass with the low-E coatings between.  The diffusion, or transmission, of light through these windows is clearly seen here.  Almost like a pair of sunglasses!

We have all seen windows where the seal has broken.  We can tell because there is condensation or cloudiness between the panes.  This anomaly will get worse and worse.  The only fix is to replace the glass.

To the right is a thermal image of a window with a broken seal.  Missing its gas the two panes are drawn together and the cooler air outdoors is visible as a purple area where they are nearly touching.  We thermographers call this a bull's eye pattern.

That all by itself is testimony for having a thermal image examination of your house during any energy audit.  No self-respecting energy auditor, like me, would forget thermal imaging!  I do this on one-year inspections too.

My recommendation:  When a home is advertised as having efficient windows, ask the U-factor and what the solar gain is!  You will impress, or befuddle, the sales people!  And probably your construction supervisor too...

 

Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560

www.jaymarinspect.com


Comment balloon 19 commentsJay Markanich • June 26 2010 06:45AM

Comments

Jay.....that was a great post.....very informative and I learned info that I did not know.....thank you....

Posted by Barbara Todaro, "Franklin MA Homes" (RE/MAX Executive Realty ) about 8 years ago

  I wish Santa or Uncle Sam or someone would bring one of our inspectors one of those handy dandy cameras...sooo good to know where your energy dollars may be going...

Posted by Sally K. & David L. Hanson, WI Realtors - Luxury - Divorce (EXP Realty 414-525-0563) about 8 years ago

Barbara - a mind stretched by a new idea cannot return to its original form!

S&D - thermal imaging cameras are amazing.  There is so much that can be learned from them.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 8 years ago

Thanks Michael!  But I am not the go to guy for that other Windows thing!  My son is a lawyer for Microsoft - you might try him...

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 8 years ago

Thanks Jay as always you have information that most of us wouldn't even think of unless we were in the business. Come to think of it most inspectors probably don't have that fancy camera you have for measuring thermal temperature.

Posted by David Okada, Service-Beyond Your Expectations (Douglas Elliman Real Estate) about 8 years ago

You are right, David, most don't.  And it takes a lot of training and practice to get it right.  Thanks for your kind words also.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 8 years ago

Jay, Informative it was...The tip about putting your hand on the window during a hot sunny day and it feels cool is a good sign...Thanks for Sharing, Jen

Posted by Jennifer Dulmaine, Seth Campbell Realty Group (Keller Williams Realty) about 8 years ago

Thank you for the very informative information on windows! Thank Active Rain for making it possible.

Posted by Sam White, Integrated Marketing - Bryan College Station, about 8 years ago

You are welcome Jen!  We aim to please!

Sam - You need some low solar gain down there, don't you?

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 8 years ago

Jay, Thank you for such an informative post.  I am re-blogging it.

Gloria

Posted by Gloria Todor, & Doug Durren (484) 431-3686 in SE PA (Century 21 Absolute Realty ) about 8 years ago

Thanks Doug and glad you enjoyed it!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 8 years ago

Jay, A wonderful informative blog post.  Great information. 

Posted by 1 ~Judi & Don Barrett & Chassy Eastep - Integrity, BS Ed, Integrity Real Estate Services -IDABEL OK (Integrity Real Estate Services 118 SE AVE N, Idabel, OK 74745) about 8 years ago

Thanks Judi.  I also thought it was an instructive blog!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 8 years ago

Thanks for the information and the picture.  Looks pretty neat.

Posted by Gene Allen, Realty Consultant for Cary Real Estate (Fathom Realty) about 8 years ago

When I saw that light pattern on the floor, Gene, I thought it would make for an instructive post.  So I moved the windows to create a nice even pattern for the photo and took it!  Glad you enjoyed it.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 8 years ago

Hi Jay, good information.  You caught the importance of the right window for the climate.  A window designed and manufactured for a southern climate installed in Vermont will not perform as well as window designed and manufactured for a northern climate. Net to me low U-factor is always good while for the Solar Gain Transmission Factor it depends.  

Posted by Dale Ganfield about 8 years ago

Thanks Dale.  I thought this was a very instructive post and would get a bit more attention!  I wonder how often builders mix and match the wrong windows!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 8 years ago

Thanks for providing this information. Good luck and more success!

Posted by Mike Warren (Real Estate) about 5 years ago

You found an oldie but a goodie Mike!  Glad you did and stopped by!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 5 years ago

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