Prefab house from the 70s: only 13 cm wall thickness?!

Enlighten me: what exactly is the deal with these window construction years?

Between 1990 and 1995 (or so...) was the time when you could find uw-values between 3.x and 1.x (so significant energy innovations in the industry)?

The change of ownership is likely to lead to a replacement requirement for a 30-year-old gas boiler.

Enlighten me: what exactly is the deal with these window construction years?

From 1994 on, windows were only installed with thermal insulation glazing. The inner side of the inner pane was coated with a vapor-deposited layer that reflects infrared radiation back into the interior. This reduced the U-value of the glass portion from about 3 to 1-1.5 W/m²K compared to the insulating glazing used previously since the 1960s. There is a lighter test that can be used to find out what is installed in case of questionable construction years (1991-1994).