On Mon, 02 Jul 2012 19:06:43 -0400, clare wrote:
I understand in Siberia, a "mud room" is common to every house, as an
opening of any door can lose a huge amount of warm air in a few seconds.
They are an intentional barrier against arctic conditions, and have two
doors.

That is what you call an "air lock" - which IS one function of a
mud-room.

We call ours a "dog lock"; it stops the critters escaping when coming
into the house.