Heating screed with device vs. with heat pump: costs?

The term "21 days" in DIN En 1264-4 under point 4.2.4 refers exclusively to the waiting time of a cement screed after its installation before it should be heated up.

Our cement screed was completed last week. My construction company now wants to start the heating phase via the underfloor heating/LWWP next week (after about 10 days). Isn't that 11 days too early? They said that's always how it's done, and there were never any problems. Should I insist on waiting and postponing all other trades?

"My construction company now wants to start the heating-up phase next week (after about 10 days) using the underfloor heating/air-water heat pump. Isn't that 11 days too early?" That depends. Specifically, on what the manufacturer of the binder says. There are cement screeds that can be subjected to functional heating earlier than after a waiting period of 14 days. If heated too early, the cement stone does not yet have the necessary strength – and then it tends to develop obvious cracks. That would certainly not be a "fatal flaw" with individual cracks, but if the screed is deprived of the mixing water necessary for hardening too early, it cannot achieve its final strength. So better to ask and have the manufacturer's confirmation shown. Regards: KlaRa