Have talked with a couple of engineers from two major door manufactures and both seem to think it is a doable install if you have the wall depth and a couple of other layout considerations resolved. Vapor infiltration is possible(but mitigated by being fiberglass doors, and it must meet your local codes. So I feel OK in going this plan for my egress from attached garage to new living space. Is it possible to "weather(air infiltration0 seal" lock sets to any extent??

Here is my grandma's double door:
http://ecorenovator.org/forum/attach...1&d=1407126460

I had my IR thermometer with me, so I did a quick check of the temperatures. The temperature of the entry hallway was 25.5°C, the inner door's inside/outside surface temps were 26.5/27.7°C, the temps for the outer door were 28.2/30.4°C, resp., the outdoor temperature was 31-32°C.

With only ~6°C difference between indoor and outdoor, the effect of a double door does not show that much. In the winter I should get data with a 20-30°C temp difference.

Are those solid wood doors though? Granted the aesthetics wouldn't be as nice but using a urethane core door instead of either one or both of the wooden doors would likely be an improvement. I think one urethane filled door might outperform two wooden doors plus the air gap. Even better if both were urethane core. I can't tell too well by the picture but I'm not seeing any gaskets on the visible door.

A double door like that is going to be annoying to use and I would only install one in a very low traffic area.

Going to a garage, you already have one air lock, the garage door, so the seal of the entrance door you install is going to get very little stress.

Having two doors like this is also going to cause you to leave both of them open longer, letting more heat out, as you fumble with both doors, so if you end up using this doorway very much it might end up being a larger heat loss then planned.

Wood they are, Grandma would not accept anything less natural.

The entrance hallway is already an airlock. If visitors are expected, then the internal door can be left open and the setup works as if there was only one, external door.
I know from years of practice that if you have both hands free, then you can minimize the time that the doors are open, reducing drafts: When opening the second door, I am already closing the first door behind me.