First of all I live in Japan where homes are not centrally heated or cooled. My plants (peppers and tomatoes) live in our attic storage area which as no cooler/heater and temperatures on average fluctuate between 5C (41F) at night and 18C (65F) during the hottest part of day throughout winter. Also my windows are double paned and not gas filled.

Given these conditions, would it be feasible to harden off plants in front of a south/southwest facing window with perhaps a fan nearby?