The figure came out of the 40CDi brochure.
You are not the first to comment on the high heatloss. The property has 180m2 and 565m3 of air due to 4,1m ceilings. There are two internal patios and 20 balcony windows 2,1x1,5m.
Calc based on following materials:
Windows 1,50 W/m²K
Ext wall...