Nogent-sur-Seine has two P'4 reactors, 1310MWe each, or 3930MWth (satané Karnaugh), for a total of 7860MWth. The values for a pair of EPR2 reactors are 1750MWe for one unit, 5250MWth, and 10.5GWth for two units.

The total heating requirement of Paris at peak demand in the middle of winter is 10GWth (for electric heating the only non-negligible inefficiency is inside the reactor itself, for gas and oil heating the energy inefficiencies are out of my scope here).

The question is this:

Can we 3x the available heating power to Paris during winter just by adding a trenched ~100km pipe from Nogent-sur-Seine to Paris?

This would reduce electric load on the grid a lot and make centralized heating systems much more economical.

In order to math it out, I need to know:

Germany has been much better than France at refurbishing it's buildings to improve their thermal insulation. However, energy consumption for heating has not changed sensibly. The reason being the rebound effect, like with everything: people get used to spending x per month, and they continue paying the same thing. They just heat their homes to a higher temperature.

We can learn from their mistakes, and be much more labor efficient. We can reduce the cost of heating, instead of insulating individual homes.

End result from the individual perspective would be the same: spend the same, get more heat. This time because of more energy rather than better insulation but they won't be able to tell the difference.

(also such a system can be used to cool living spaces in the summer, something just switching oil and gas boilers to electric radiators can't do)

Heating is 69% of residential energy consumtion, which is itself 28% of final energy use in the country, or 19.32% of total consumption, so solving this problem alone is 20% of the country's energy consumption (with pleasant secondary effects: it lightens the demand on the electrical system, it targets a use that is mainly fossil, it participates in the series effect of nuclear, etc).