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

May I intervene in the discussion here once? Many things have been correctly pointed out so far, but other remarks were rather questionable and/or incorrect. It is true that the functional heating serves to check all components used for the installation of a warm water underfloor heating system. Since the screed is still "virgin" at this point in time, meaning that due to the contained amount of water during drying/heating considerable stresses can still build up and have not yet been relieved, this phase must be carried out stepwise, i.e. in several graduated temperature steps. So far so good. However, with surface readiness heating, it is not as "SaniererNRW123" noted, that the maximum temperature must be maintained for 21 days! The term "21 days" in DIN EN 1264-4 under point 4.2.4 exclusively refers to the waiting period of a cement screed after its installation before it should be heated. The aforementioned standard does not give any indication regarding the duration of the maximum heating phase during surface readiness heating. Neither a standard nor any regulation can do that because the object-related drying conditions, the nominal screed thickness, and also the type of binder are decisive for the drying speed. If, for example, I close all windows tightly and have an 80mm thick screed, I could heat until the "end of time" without the screed reaching surface readiness. Here, just to mention it briefly, the CM residual moisture measurement by the floor layer is crucial to determine whether the heating phase (usually a maximum of 3 days) was sufficient or if heating (and of course ventilation) must be continued. On the topic: must the flow temperature be 50°C if I later use a heat pump with 30°C flow temperature? Unfortunately, the answer here is: YES AND NO. Why? Calcium sulfate screeds must not be heated above 40°C at the heating elements. Therefore, the 50°C do not apply to this binder under any circumstances. In cement screeds, the maximum temperature after functional heating and about 3 days of waiting at room temperature should be set to whatever the heating system is able to deliver! Because surface readiness heating serves exclusively to drive out excess mixing water and has nothing to do with later use (low temperature heating)! This should basically answer the questions on this topic. Greetings and good luck: KlaRa

Calcium sulfate screeds must not be heated above 40°C at the heating elements. The 50°C limit definitely does not apply to this binder.

Question out of interest: Where is that stated?
Why do I ask? In every heating protocol (at least the ones I know), the 50-degree limit is stated. Regardless of whether from screed layers or screed producers.

For cement screeds, the maximum temperature should be set after functional heating and about 3 days of waiting at room temperature, which the heating system is capable of delivering!

And I would also like to put a question mark behind this statement. Why should I heat up to 65 degrees (which many heat pumps can achieve) to reach readiness for covering (you say after the functional heating)? To my knowledge, 55 degrees is the maximum temperature that should be applied.

However, during cover readiness heating, it is not as "SaniererNRW123" noted, that the maximum temperature must be maintained over 21 days!

Please cite my source correctly. I do not say "must," but "usually." As a rule of thumb or in most heating protocols of screed layers, +/- three weeks is taken.

Does anyone know the flow temperature the heating system is designed for? In that respect, the statement that it only needs to be heated up to 30°C is nonsense. A heat pump can also be designed for 35 or 40°C flow temperature.

Especially to get the screed dry, I would rather do functional heating at 40°C than at 30... otherwise, you’ll have to wait a few weeks longer until the CM measurement is right and lose time again.

The 650 EUR rent/month probably isn’t the only ongoing cost. Think about the loan (interest on the drawn amount without repayment, possibly standby interest). On top of that, you have to heat 2 apartments/houses this winter, which certainly won’t be included in the 650 EUR.

Heating up with heat pumps is, due to the high heating power required, by the way (largely) also done with an electric heater. So you really don’t save anything compared to the Hotboy. On the contrary, your heat pump will hardly have a 19kW electric heater, so it won’t reach 40°C or will be heavily stressed right from the start... which heat pumps really don’t like...

Above, a demand of about 6300 kWh was stated for my project, where does the big difference come from?

Central question: Is the house already insulated?

Wow, the initial question was: heating up using an external heater, or using a heat pump. That then drifts into "How does the screed have to be heated up."

So: one can discuss the heating of the screed at length, but: the specification comes from the screed installer, and if you want to keep the warranty, you follow his specifications via a protocol.

Yes, the external heater consumes significantly more electricity than the heat pump. Here it depends on the seasonal performance factor of the heat pump, which traditionally is rather poor at high temperatures. So about half the electricity that the heat pump needs. This is already eaten up by just one month’s rent.

Please also consider: the amount of heat required roughly corresponds to the annual heat demand of the house. That means your heat pump has basically been running at full load for 1 year when it is put into operation for the house. That is a real argument for the external heater.

So: option 1.

I spoke with my installer yesterday. He says with a heat pump you can’t count on it this winter anymore, he’s still getting gas heaters in small quantities, but probably not for me this year either.

So definitely option 1 if the house is to be finished by spring.