[QUOTE="R.Hotzenplotz, post: 246651, member: 26099"]The heating installer called to say that now a little more than 2 kW additional heating load is required and the offers for the heating system can probably not be maintained.
Presumably more of a problem between him and the GÜ. He says it is because the sill height of the windows was changed from 100 cm to 86 cm. However, the sizes are also stated in the contract (except for an additionally commissioned basement window, which hardly makes 2 kW).[ /QUOTE]
That is simply nonsense from him.
With 15 cm higher windows, this makes the following difference:
Assuming you have 10 linear meters of windows affected, you have 10m*0.15m=1.5m² more window area instead of wall area.
With assumed U-values of 0.20 W/m²*K for the wall and 1.2 W/m²*K for the windows and a 34 K temperature difference from 20° inside to -14° outside, that is 1.00 W/m²*K *1.5m² * 34K = 51W.
So a whole 0.05 kW more.
Wow.