The Rationel EnergySimulator will give you a good indication of how much you can save on your heating bill by changing your old windows and doors.
The process is quite simple. Put in the size of your house (in m2), when were your existing windows installed (four digits - i.e. 1978) and select which Rationel product you are interested in.
Choose source of heating
Which product series would you like your energy calculation to be based on?
Total energy saving
Yearly heat savings
The listed savings are indicative and should be confirmed by an advisor.