Is an air-to-water heat pump sensible for renovation as an efficiency house monument (160% Energy Saving Ordinance)?

Every 2 years a new compressor plus a new heat pump after 15 years. That is 21,000 EUR with a price of 7,000 EUR for the heat pump. Is district heating not an option in the area?

No. Gas is available in the street. As an alternative to the air-water heat pump, a groundwater heat pump would also be an option. It is apparently approval-worthy in the area. With all subsidies, the investment would be roughly comparable to the gas heating. For me, the advantage remains not having to be bothered with the "landlord's participation in the CO2 tax." Would a groundwater heat pump be generally better? Less maintenance? The efficiency at low temperatures seems to be significantly better.

I am not familiar with that, sorry.

Based on the mentioned repair costs and problem predictions from some here, I must consider myself lucky to have the only ever built air-to-water heat pump that runs without problems!? But it’s logical, since with the gas heating before, I had repair service in the apartment at least once a year, as it liked to give up before holidays. But well, it was replaced after 9 years anyway, because repair costs would have been higher than replacing it. Yes, the text could contain sarcasm.

Btt.: Should the OP prefer gas after all, maybe have it calculated whether better insulation than WLG 42 would be possible, in order to only install 4cm insulation even with gas?

PS: In the fifth year without a new compressor.

Wait a minute. Has our country really become that crazy? That means with a gas heating system you have to insulate so much, otherwise it won't be approved? In the end, you are financially forced to use the much less efficient and more environmentally harmful air-water heat pump?

Germany is destroying itself, this is another example of how we are driving everything into the ground...

Wait a moment. Has our state really gone that crazy? That means with a gas heating system you have to insulate so much, otherwise it won’t be approved?

Yep, it’s due to the calculation methods. With gas, the house becomes "worse".

In the end, you are financially forced to use the much less efficient and more environmentally harmful air-water heat pump?

That assessment could only have come from you ;)

What I would do:
- WLG 42 for interior insulation is the worst possible insulation variant you can buy for money
==> upgrade to at least WLG 32/35 – costs almost the same price
- Why only 4cm insulation? The surcharge for eight is low since only the material costs rise slightly – the fixed costs like plaster, labor, etc. remain the same
==> put on 8cm insulation right away (for a house of 10x10m we are talking about a loss of just over one sqm of living space)
- Recalculate with the above-mentioned insulation measures and then consider the air-water heat pump again
- Design underfloor heating consistently at 7.5cm (or less, if necessary/sensible) and check for the lowest possible supply temperature
- Air-water heat pump as a monoblock with indoor installation (regardless of whether Panasonic/Wolf/Viessmann or similar)
==> cheaper prices than split devices and especially Panasonic with great values and high tolerance against misuse/misdesign
- Include an engineering office for heating planning/design (costs about 200-300€ for room-by-room heat load calculation as well as computational and graphical design of the underfloor heating)