I had a question for the window experts out there... This is not another rant about window condensation. It seems that vinyl extrusion frame replacement windows are very inexpensive. Even with good glass (2-pane with LowE glass and Argon filled) can cost around 250.00 installed. I had Alliance Belmont installed in my apartments and am very happy with them so far. They do get some condensate but the buildings are not that air tight and condensate on the vinyl isn't as big a deal as it is on wood. The vinyl extruded channels are hollow and not as energy efficient as they could be. I like to use cellular blinds but they insulate the window a lot and cause even more condensation. Considering the installation wouldn't be much more, how about installing two of the inexpensive vinyl windows, sandwiched together, with their frames caulked together? On the exterior it could be a single hung and on the interior a double hung to aid in cleaning and accessing the lock on the outside window. Now you have 4 panes of glass, double frames, and 1/2 or less the air infiltration. It seems like the dual-window would be about R-7+ (U-Factor of .13) and cost about 350.00 installed. This would be the most energy efficient window at the cost of some major brands bottom-of-the-line windows. What do you think? Would it work? We build with 2x6 walls up here so there is usually a 4 inch jamb extension on windows so there should be plenty of room for two window thicknesses. Vinyl replacement windows are usually 2 3/4" thick. Issues I foresee:
1. More difficult to clean and get at the lock on the exterior window
2. Heat gain between the two window units
3. If you have the window open when it rains and you get water between the two units.
4. You have to open two windows instead of one. I guess that is not much different then opening a combination storm/screen that some have installed on older single pane windows.

Some history on why I'm thinking about this: As a home owner that purchased good Energy Star (.28 U-Factor) windows with LowE and Argon filled AND run a fresh air exchanger 24 hours a day to keep the relative humidity around 33%, I'm frustrated that I can't keep the moisture off my windows. I built three years about and installed vinyl clad with oak on the interior. The oak is turning black and the vanish is peeling off after only 3 winters. I paid $400-500 per window without installation. Up here in Northern Wisconsin we have -30F temps and I understand I WILL have condensate on those days. But when I went to research windows, your glass options are very limited and the price gets astonomical. There are 3-panes of glass or the plastic film between the two panes of glass for an R value of maybe 6 instead of 3 but those are available on top-of-the-line windows and probably cost 800.00 per window. Plus the frames/sashes aren't any better and the air infiltration is the same, so there is still no guarantee against condensation.

 

What would you use for an inert gas for between the units? Anything but an inert gas will absorb moisture and will condensate between the panels. So no, it won't work. Vinyl windows still offer the best hedge against the problems you see with wooden framed windows. The hollowness of the vinyl frames actually insulates, since it captures air. A solid frame will telegraph heat and cold from the outside to the inside more readily.

 

Thanks Chandler for pointing out the potential condensation between the two windows. I think you are right it could happen but I wanted to clarify that the windows are not sealed together. I said caulked in my original post but meant the frames were caulked together during install. There is always some air infiltration/movement between the two window units (not the sealed dual-pane glass in each window unit). I was thinking the condensation between the two window units would be similar to applications that have shrink plastic on the interior or a storm window on the exterior.

 

I tried a storm window to test for condensation. I thought that since the interior window has much less air infiltration than the exterior storm window, the air between the storm and interior window would be exchanged often and be at the same humidity as the outside air. Boy was I wrong! Once some moisture and condensation gets in there, it freezes and frosts the window every morning. Can't see out.

I imagine it would be much worse with my two vinyl window idea. So if you found this post, thinking about trying the same thing, you really have to figure out a way to keep the moisture from in between the two windows.

 

Sometimes it's book learnin', sometimes it's OJT.