My hubby is a carpenter, he has installed double paned windows as well. The insulation is top notch. Winters here are fairly ok..sometimes it gets below 30.
The windows are amazing how effective they are. The people who installed them are a father son team. First the son measures each window and then they order the windows made to the millimeter. Then they can install a ton of windows in a day. We don't even hear the barking dogs any more.