It's cold when you're in a t-shirt, and haven't been in a proper warm house all day :(
I was in Austria, Germany, England AND Ireland today. How fun!
My house also hasn't been lived in for about 12 days now, and my parents just went straight to bed when they got back from the airport with myself and my sister.
I consider 13-18 degrees plenty warm though.
Also, however, my upstairs is always 3 or 4 degrees colder then downstairs.