A blog post

R5 vs. R3.33 Windows

Posted on the 22 June, 2009 at 4:07 pm Written by Gwenael Hagan in Energy & Window Performance

Last week I participated in an Alliance to Save Energy webinar entitled “Window Energy Efficiency Beyond Business As Usual”. The webinar touted the benefits of super high performance R5 windows over commercially available R3.33 windows. The Department of Energy is pushing a volume purchase program to help drive the cost of R5 windows down to an acceptable premium.

I think continued evolution in window, door, and skylight performance is good for everyone and will force the better companies to increase the speed of innovation, while weeding out the lower quality/lower price players. I am not sure I agree that a DOE-sponsored volume purchase program is the best public/private partnership, but I remain open-minded.

What I am sure of is that with very few exceptions, the cost of today’s R5 windows is not at all justified by the energy saved or the carbon reduced. This remains true even if you double today’s cost of a therm (100,000 Btu)

The attached presentation puts the R5 vs. R3.33 debate in the context of Boulder City and County building codes and amplifies the “cost efficiency” of commercially available windows. While I take complete responsibility for the content of this post and the presentation, special thanks are due to David Neiger and the Populus team for helping work through the energy calculations.

hers-building-codes-and-windows

some comments

There are currently 4 of them
  1. George Eckerd 13 November 2009 at 10:39 am permalink

    We have a fiberglass R5 window now.

    We are a window manufacturer in Toledo, OH.

    Our new web site will be up and running next week. existing site is http://www.comfortlineinc.com

  2. Gwenael Hagan 13 November 2009 at 11:31 am permalink

    There are a number of R5 fiberglass window manufacturers. The elevation of Toledo averages 600 feet. How would you supply a metro Denver market with elevations of 5,200 to 6,500?

  3. dan 15 December 2009 at 7:50 pm permalink

    Many vinyl windows can easiliy get the R% with a triple. Many 1″ IG with Argon even. The elevation change of 4600-5900 should not effect a well made IG. over 7500 change would however.

  4. Gwenael Hagan 29 December 2009 at 12:25 pm permalink

    Vinyl is the weakest window frame material from a rigidity perspective – as compared to fiberglass, aluminum, or wood, has the highest expansion and contraction ratio, and is the most susceptible to deformation due to heat. Given all of that, I would be very uncomfortable looking a customer in the eye and telling them the added weight of triple glazing won’t have negative mid- and long-term consequences. I say this even in light of the “lifetime” parts and labor warranties offered by many vinyl window manufacturers.

    On 1″ IG (insulated Glazing Unit), the glass manufacturers have determined that a 1/2 inch airspace is optimal for dual glass units so I don’t see the advantage of a 1″ IG over the standard .75″ IG.

    I agree with your comment regarding well made IG and elevation changes of 4600 to 5900. We offer Marvin’s Integrity fiberglass windows which are manufactured in Fargo and shipped to us in Colorado for distribution throughout the front range and lower elevation mountain communities.

    These types of discussions always bring me back to the misplaced focus some in the window industry have on the pursuit of R5 windows. If you double, triple or quadruple today’s energy prices, there are many energy efficiency measures that offer much improved return on investment.


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