ᐅ KfW55 Radiators with Air-to-Water Heat Pump or Gas Boiler?

Hello everyone,

here is the starting situation:
1.5 floors
125 sqm (1350 sq ft)
36.5 cm (14 inches) Ytong blocks
gable roof with 45° pitch including dormer
a decentralized heat recovery ventilation system is also planned.
and if I understood correctly, a primary energy demand of 77.3 kWh/m² (7.18 kWh/sq ft) or another figure of 22.2 kWh/m² (2.06 kWh/sq ft) according to the energy saving ordinance. I assume the second figure applies?

We will probably install radiators (underfloor heating is likely ruled out for now, reasons are not that important at this stage) and our general contractor recently said it might be possible to operate the air-to-water heat pump with radiators. I don’t have much experience here. I know that with an air-to-water heat pump, the flow temperature should be as low as possible.

So the options are:
An air-to-water heat pump (Rotex HPSU Compact 308) + radiators + a "small" photovoltaic system (I'll arrange this myself)
or a gas boiler + solar panels about 5 m² (54 sq ft) (Vaillant auroCompact, size between 3.3 and 14.7 kW still to be determined, including a 150-liter (40 US gallon) stratified storage tank) + a somewhat smaller photovoltaic system (due to space needed for solar hot water).
What is not entirely clear to me is whether the solar panels also cover heating or only domestic hot water.

Which solution would make the most sense in this situation? Advantages / disadvantages?
Currently, I tend toward gas, even though we still have to budget for the gas connection costs here.

I briefly spoke with the photovoltaic provider as well... he said that under the new 2016 regulation photovoltaic systems are taken into account... unfortunately, he only has his training next week and can give me more details then... in his opinion, that might make the solar thermal system unnecessary and we could install more photovoltaics instead.

Best regards to all

why no underfloor heating?

Best regards
Sabine

Why not here as well?

Underfloor heating and an air-to-water heat pump is actually one of the least efficient combinations you can have... plus photovoltaic panels and/or solar thermal...

Is someone trying to throw money away?

Okay – that would mean if I interpret your answer the other way around:

The better combination in this case would be: GAS theme

Not necessarily, it just needs to match the rest of the house... but what definitely does not fit are the radiators, because for them to work effectively, they either have to be normal size and supplied with water at around 60 degrees Celsius (which in a KfW55 house probably means a sauna), or they are supplied with only about 35 degrees Celsius and then need to be about 2-3 times larger than usual to heat the rooms properly.

And regarding the rest... more is not always better. A little photovoltaic here and some solar thermal there does not mean it becomes cost-effective (unless the systems are free of charge).

The lower the supply temperature, the more radiators you will need. I see gas heating as the primary option here. It won’t exactly be a sauna, but you’ll have small, handy radiators.

But still: why not underfloor heating?