Pretty Good Windows for Zone 4
pdadamery
| Posted in General Questions on
Hi all,
We are building in central Virginia (zone 4). We’ve been researching windows that will get us into the “pretty good house” performance range without overshooting our climate zone needs. The Canadian windows look great, but seem like they might be overkill. Any recommendations for windows that would help us reach our energy and sustainability goals without breaking our budget?
Thanks for the help,
Phil
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Replies
Phil,
In Climate Zone 4, it's usually hard to justify the upcharge for triple glazing. That said, some double-glazed windows cost more than triple-glazed, so there are a lot of variables.
For a pretty good house in Climate Zone 4, windows that comply with Energy Star requirements will probably be satisfactory.
In zones 4 & 5 double low-E double panes with the usual low-E coating on surface #2 (the inward facing side of the exterior pane) , and an additional hard-coat low-E on surface #4 (the interior surface that is in contact with the room air) is a good value- nearly the same performance as a triple pane, but at much lower cost.
With argon fill (instead of air0 U-factors are in 0.20-0.22 range. Depending on the surface #2 coating the SHGC greater than 0.5 for heating season solar tempering where desired (such as south facing windows with properly designed roof overhangs), or less than 0.25 to limit solar gains where desired (say, on west facing windows that are difficult to shade on the exterior.) Some examples would be Cardinal glass LoE180+ i89, good solar tempering glass, their loE-366 + i89 has pretty good heat rejection while maintain decent visible light transmission. (see: http://www.cardinalcorp.com/source/pdf/tsb/ig/IG05_01-2016.pdf )
The low-E coating on surface #4 lowers the temperature of the interior surfaces which in colder climates can result in copious condensation during cold snaps. Due to the high emissivity of water, performance drops considerably when there is condensation on the glass, rendering the coating on surface #4 useless until the moisture evaporates. That makes it a poor choice for zones 6 & higher, since there will be periods during cold snaps where the surface of the glass dwells well below 40F for days, making condensation all but certain that the window performance drops when you need it the most. But for zones 4 & 5 those events are rare.