Sorry, no triple panes. All the windows are Jeld-Wen Siteline EX units with northern Low-E argon-filled insulated glazing.

Great! Thanks! Do you know if its a HUGE difference going to triple? I guess $ wise it is... Did you design the space based on size of available windows?

For cost reasons we used the biggest non-specialty picture units that Jeld-Wen could manufacture. They're roughly six feet wide and eight feet tall.

As for glazing and insulation, here's my take on the whole thing: windows have a pretty lousy insulating value no matter what kind you use. Single, double, or triple-glazed windows will have a small fraction of the insulating value of a wall. Do what you can within reason (whatever you think that is) to get the best glazing possible for the money, and then insulate the dickens out of your walls and floors.

This house has a conditioned, insulated crawl space, there is exterior insulated sheathing on the outside of the studs, and the wall cavities and the roofline are insulated full-depth with closed-cell foam. It's a pretty tight envelope. We were also very careful to caulk and seal as tightly around the window and door openings as possible. Limiting air infiltration is half the battle. Of course, make sure you provide for fresh air exchange when you've got a very tight envelope.

The owner has reported that the house is easy to keep warm, even in very cold weather. And it's being done with conventional heat-pump forced air units (we went all electric since the roof is covered in PV solar panels).