what is an Icelandic home's average room temperature?
Regardless of geographic location, the preferred room temperature is between 20 and 22 C, and depends upon the individual.
There is an excellent answer from an Iceland authority here:
http://icelandreview.com/ask_eyglo/What_is_the_average_room_temperature_in_an_Icelandic_home_in_the_wintertime__2_374466.news.aspx?ew_news_onlyarea=1000&ew_news_onlyposition=2