This is standard enough practice for developments. It's less about the floors but more to speed up the drying of plaster for painting etc., and gets the builder out of the property faster. And the Heatpump (or other heat source) will be on a lot for commisioning, plumbing, balancing etc. It's also a safety thing whereby they don't want to be leaving windows/doors unlocked open 24/7 on site to allow the same drying. But it's not like the it is on at a high temperature, 15/16 degrees maximum to gradually dry out plaster before painting.
@TestyUser1 , for reference we moved into a new build in Febuary a few years ago. Electricity was commissioned 3/4 months before that with Heatpump running soon after so cold temperatures with heat on. ESB was transfered to us with meter reading on day of handover. In that time it had used approx 2400-2500kWh. No question whatsoever about us contributing although that was well before the big increase in electricity costs
As others have said, this is the builders cost to bear unless it is specifically called out in the contract. The trades you mentioned could not have used much more than 200 units so even in the worst case scenario at €0.40/unit, your 'contribution' is less than €100. They are just trying to pull a fast one and see how many just go along with it an pay up.