Is the heating oversized?

Good day,

after the first days in the new home, the heating is giving me a bit of trouble. Somehow I have the feeling that something is not running 100% there... it heats very irregularly. In my perception, only when as many rooms as possible are set to flow. Once most rooms have reached their temperature and only 1-2 are open, it quickly cycles up and down...

- we have about 140 sqm of floor space
- underfloor heating throughout the house
- a Junkers Cerapur ZBS 22/100 S-3 MA gas boiler with hot water preparation (22 KW)
- 17.5 cm calcium silicate brick + 14 cm [WDVS] (no special energy saving regulation)

As mentioned, if only a few heating circuits are open, the boiler switches on (from about 25 degrees flow temperature), heats up very quickly (up to about 45 degrees flow temperature), then quickly drops again and switches on again. The heating circuits are therefore only sporadically heated...? If I open more heating circuits, the heating time takes longer and it gets warm... is it oversized because it heats individual rooms poorly?

Has the heating system been put into operation with all the necessary inspections, acceptance certificates, and specialist contractor certificates, including the hydraulic balancing? Has a heat load calculation and system dimensioning been carried out beforehand? The burner capacity seems oversized to me. Roughly calculated, the heat generator should have approximately the capacity of (140m2 x 70 W/m2) + (4 x 200 W for hot water preparation/4 persons) = 9800 W + 800 W = 10.6 kW.

With 22 kW burner capacity and a possibly too small buffer tank, the unit cycles frequently. This can happen if the entire system has not been planned and dimensioned. Contact the heating specialist company or the general contractor/subcontractor who built the house, complain about the insufficient capacity, and request the necessary calculations and the above-mentioned specialist contractor certificates.
You are within the warranty period of 4 years/VOB or 5 years under the Construction Code and have hopefully enforced a warranty retention of at least 5% of the invoice amount for such cases.

Why does it even heat up to 45 degrees? In my opinion, lower the heating curve and open the thermostats further or fully. 22KW is of course very generous.

Moin Moin If I remember correctly, I’m not really familiar with Junkers, the heating curve can only be turned down further in the professional level, or the option to do so can be set. Furthermore, it is also possible in the professional level to reduce the power during heating operation via the fan speed. Olli

Has the heating system been put into operation with all necessary inspections, acceptance certificates, and specialist contractor certificates, including the hydraulic balancing? Has a heating load calculation and system dimensioning been carried out beforehand? The burner capacity seems oversized to me. Roughly calculated, the heat generator should have approximately the capacity of (140m2 x 70 W/m2) + (4 x 200 W for hot water preparation/4 persons) = 9800 W + 800 W = 10.6 KW.

With 22 KW burner capacity and possibly a too small buffer tank, the device cycles frequently. If the entire system has not been measured and dimensioned, this can happen. Contact the heating specialist company or the general contractor who built the house, complain about the insufficient performance, and request the necessary calculations and the aforementioned specialist contractor certificates. You are within the warranty period of 4 years/VOB or 5 years Building Code and hopefully have enforced a warranty retention of at least 5% of the invoice amount for such cases.

Which item in the calculation are the 70 watts you mentioned?

[*]Primary energy
[*]Final energy
[*]Heating demand

I have shown three items for myself.

Why does it even heat up to 45 degrees? In my opinion, lower the heating curve and turn the thermostats further up or fully on. 22KW is of course very generous.

The temperature fluctuates, it depends on the outside temperature...there is a separate sensor on the outside wall....but it is always around that range. The room controllers are almost all set to 20 degrees...

Hello Hello If I remember correctly, I’m not really familiar with Junkers, is it only possible to turn the heating curve further down in the technician level, or enable the option to do so. Furthermore, it is also possible in the technician level to reduce the output during heating operation via the fan speed.


Olli

And what does lowering the heating curve achieve?

Has the heating system been commissioned with all necessary inspections, acceptance certificates and specialist contractor declarations including the hydraulic balancing? Has a heating load calculation and system dimensioning been carried out beforehand? The burner capacity seems oversized to me. Roughly calculated, the heat generator should have about the output of (140m2 x 70 W/m2) + (4 x 200 W for hot water preparation/4 persons) = 9800 W + 800 W = 10.6 KW.

I have an acceptance certificate from the chimney sweep as well as a specialist contractor declaration...for all others I would have to check.