Lower U-Factor = more efficient. Its the INVERSE or R-Value.

Condensation RESISTANCE higher = more resistant to the formation of condensation.

Where is the home...climate wise?

Chicago high-rise, waterfront building

I would go triple. No doubt. Not sure they have an offset glazing option in triple, but them temp would have me leaning in that direction.

My apartment is really warm in the winter because of the radiator? Does triple pane necessary?

What does an offset glazing option do?

Offset is for noise. I know they make it in double pane. If noise is the bigger issue, go that route.

none of the contractor I talk to tell me what these stuff mean! I asked for CPD number, one of them don't know and said they can't give it to me. Ask me why do I need it? I asked them who is your distributor. They said why do I need to know. We give you the window. We build it.

...Me scratching my head... I'm just a homeowner who'd like to know everything if i'm going to spend 20K for 8 windows :(

Find a new contractor if they can't tell you what offset glazing is.