Plavecsky's Ponderings By Jim Plavecsky
by Jim Plavecsky
March 14th, 2011

Another Game Changer

For months now, I have been hearing about how window manufacturers are going to coming out with dual-pane R5 window designs, incorporating two lites of low-E glass: one coating on the number 2 surface and a second, scratch-resistant coating on the number 4 surface, which is the surface closest to the living area of the dwelling into which the window product is installed.

Wow! This gives us an R5 window without the need to use triple-pane insulating glass! No worries about beefing up the window frame and hardware components to accept the heavier weight of triple pane IG units! And no worries about argon or krypton gas-fills in a triple pane configuration with twice the likelihood of seal failure and subsequent gas loss! It sounds too good to be true!

Well, a wise man once said, “If it sounds too good to be true then it probably is, and the reason why this is the case here is because of condensation resistance. Heat is transferred through an IG unit via convection, radiation and conduction. By putting low-E coatings on the surfaces on surfaces 2 and 4, radiant heat does not cross through the airspace of the IG unit. It gets bounced back from inside the room and bounced back from outside the house. This means the air or gas contained within the IGU stays colder especially if a metal spacer is being used which conducts additional heat from the warm side to the colder outside of the window. The result is a window unit with a very low U-value, possibly R5, but with a colder glass surface on the inside pane, which unfortunately spells “c-o-n-d-e-n-s-a-t-i-o-n.”

Now what purpose would it serve to advertise and sell a “high-performance window system” featuring R5 window ratings, only to get calls from disappointed and angry homeowners about condensation problems during the winter months!

In order to address this issue, the R5 Volume Purchase Program, which has recently been re-named the “High Performance Windows Volume Purchase Program,” has now added a minimum condensation resistance (CR) requirement of 50 for residential primary windows.

I called several of my contacts who make and sell insulating glass into the residential market to get their take on this. Their immediate reaction was that window manufacturers should be prepared to purchase or fabricate a greater percentage of triple pane units in order meet this upcoming R5/CR50 market demand that will likely be created by the HPW Program.

 We are likely to see a much greater percentage of triple- pane insulating glass including argon and krypton gas fills in order to meet the needs of HPW program. Many window manufacturers disappointedly report that the program really hasn’t taken off yet but still feel that it is likely to in the not too distant future.

Why? The DOE is apt to put more pedal to the metal as it relates to driving improved energy conservation, especially given the recent events in the Middle East which serve as a refresher course on why our nation needs to reduce our dependency on foreign energy reserves!

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  1. Hi Jim,

    Whew… at first I was scared that you were going to say how great the use of surface 4 Low E is. I apologize. I should have known better. In addition to the condensation issue, I still am not convinced that the exposed Low E won’t disappoint in other ways. It will take a lot of success in the field to convince me that homeowners won’t find creative ways to scratch it when they clean it. There is nothing so scary as a housewife or househusband with a piece of steel wool….. Glass manufacturers have a habit of underestimating what can happen when exposed coatings meet the homeowner. I can tell you some “self cleaning glass” stories, but you probably know them already.

    In any case, keep at it.


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