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.
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
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?
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.
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.
Interesting. You are all correct, yet not at all. It is obvious that you are leaning in the direction of your supplier or manufacturer. Marvin is OK at best and is one of the reasons window standards were lowered to R3.3 instead of R5 are not where they should be. The 2 other big boys are at fault as well. We are all at fault..we voted our congressman in and I am sure they really do not care, except for how it will effect them! Enough said.
7 things come to mind:
1)it is the “total WINDOW Rvalue” that you are looking for, not just the “Center of glass Rvalue. Anyone can get to an R5 with various technology today. What about air infiltration, head and sill weatherstripping? how durable are they? In high quality glass, the weakest link in the total window is now the frame! What is being done about that? Questions, questions, they go on.
2) breather tubes, which keep the proper amount of gas needed in place, are readily used for transfer from high to low altitudes and back. That problem was fixed back in the’70′s.
3) Optimum dead air space is not 1/2″, but rather 13/16″ and it might be somewhat more now that spacer systems have improved.
4)Vinyl is the weakest of materials, but it has a place in the industry…it is affordable and most quality Vinyl windows will outperform most wood windows and some Fiberglass units in all aspects except strength and life. What is the life of a window? I have read in Consumers Report that Wood is a 12 – 15 year life; Vinyl is good for 31 years; and Fiberglass for 80 years.
5)In the grand scheme of things, it does not matter how much one family saves, but by multiplying millions of windows over many applications, we can and will save a bunch of energy.
6) If you took a house that needed various energy updates and had single pane windows and had $15000.00 to spend on energy savings methods, Insulation, HVAC, etc. You would get your biggest payback from using that money to buy R5 windows. Not from insulation, not from anything else. This may vary from climate to climate.
7) Last year I installed R5.7 windows in my house in OH. I also buttoned up my insulation and stopped most air leaks as best as practical. My Gas buget had been $220.00 per month for a couple of years. After 1 1/2 years it is now $77.00. We did not lower our thermostat. I am upgrading to more attic insulation and a newer hi-efficiency furnace soon. I am interested in seeing what happens.
I am obviously biased toward Marvin and Integrity.
You are right about total window unit and air infiltration is not discussed enough. All windows are tested for this important value but not all test results are disclosed. Marvin and Integrity have them on their websites.
Breather tubes do regulate pressure as a window moves up in altitude. However, once the genie (argon or other gas) is out of the bottle, it ain’t coming back. Now some companies place a balloon over the breather tube and suggest that the gas from the balloon will go back into the window… Convinced??
Vinyl does have an important place in the market. Our point is that the combination of our semi-arid climate and high altitude compromises the life cycle of vinyl. We routinely replace vinyl windows that are 12 – 15 years old.
On your point six, i have seen a lot of models run in our northern Energy Star Climate and as much as i like to sell windows, i have not see a case where the biggest bang for the buck did not come from air sealing and insulation. Where I agree with you is that single pane windows, particularly in aluminum frames, come as close as it gets to providing a payback on energy savings alone.