ᐅ Heating Capacity Calculation and Selection of the Heat Pump

Hello! We are currently building a single-family house to KfW40 standard and are supposed to have a Bosch air-to-water heat pump installed. Our heat pump was ordered back in December 2022, but it has not been delivered yet, and there is no clear indication of when it will arrive. Our construction company now says they can install the same model (Compress CS7400iAW ORMB-S) within two weeks, but with lower capacity, specifically 5 kW instead of 7 kW. According to our heating load calculation, our house requires 2.8 kW without hot water and a total of 3.4 kW including hot water. So, it seems that 5 kW should be sufficient. The question is – is this really the case, or am I misunderstanding something? Or should we wait for the 7 kW unit, even though delivery is completely uncertain? We are a family of five living in Schleswig-Holstein. I also asked about alternatives, for example, an air-to-water heat pump from Vaillant. I was told that this is an option, but it would have to be ordered new, with a delivery time of about three months, which should be more certain. Could someone recommend: take the 5 kW unit, wait for the 7 kW, or go with the Vaillant?

An oversized heat pump is not ideal. Why not an even smaller one?

I agree with the idea—why not go even smaller? Actually, a domestic hot water heat pump and a split air conditioning system for the cold days would be sufficient. You would save a lot of money and be able to cool in the summer.

With 7 kW, you have been given poor advice.

The 5 kW unit is actually better than the 7 kW one. Therefore, choose that one or an even smaller size.

Without knowing your house, it’s difficult to say – but the 7 kW was definitely too large.

I would go with the 5 kW and look forward to moving in soon.

Thanks to everyone. Now I feel reassured.