Extra meter for heat flow tariff (heating electricity tariff) yes/no?

Oh ok, then I probably won't have to purchase 2000 kWh.

You just invested 500,000 +X € in your house, so I wouldn't worry about buying 100/200 kWh more electricity. And about 8kW, that modulates. We have just been through our flood of the century and might be waiting for the winter of the century.