Is it worth paying the extra cost for KFW55 or not?

Hello community!

We are building with highly insulating thermal bricks, but only to the Energy Saving Ordinance standard. No KfW55 so far, only KfW70 if you will. The extra cost for better insulation is €7800 plus either a photovoltaic system or 4 decentralized fans.
(So we do not have a centralized controlled residential ventilation system. That's a topic on its own. My wife doesn't want it and money is tight.)
You have to deduct a €5000 subsidy, but also add €1500 for the KfW certification again. The subsidized interest rates bring no advantage or are worse than what you can get otherwise.
In the end, about €8000 extra costs remain that you would have to save with energy.
1. Does it take forever? What do you think?

KfW55 will be legally mandatory in 2021. Soon our house would be energetically outdated and probably worth less. However, KfW70 was also subsidized two years ago and is actually already pretty good!?
2. Even if it might not be worthwhile from a calculation perspective today, would you still opt for better insulation?

3. Can an air-water heat pump (air-water heat pump) be operated without problems in an Energy Saving Ordinance standard house, or is it then a power guzzler?

Pump heating also works in KfW 70. KFW 55 is achieved through a bit more insulation and expensive technology. The house itself does not get any better because of that. Leave it. Save the money there and do something for forced ventilation. If your wife doesn’t want the air system, then take a Helios humidity-controlled exhaust motor per floor, preferably placed in a bathroom. In addition, a Regelair forced ventilation module in each window. The money should be there. The new houses are simply too tight to do nothing. Karsten

With us, the central controlled residential ventilation was fixed and the interest rates for 20 years ZB at the KFW were at a record low, so we went for KFW 55, it paid off. Today I would build according to the Energy Saving Ordinance. There is not much difference between KFW 55 and the Energy Saving Ordinance, the savings per month are not that huge. However, I would pay attention to the ventilation option.

3. It will probably consume a little more, but not a lot more either. Why do you want an air-to-water heat pump?

Thank you for the answers so far.

Why do we want an air-to-water heat pump?

I hadn’t questioned it until now because we also wanted KfW55, and not radiators but underfloor heating, and the air-to-water heat pump is so common and advertised.
Otherwise, a gas boiler with condensing technology would be included in the basic price.
The surcharge for the air-to-water heat pump is €6900 compared to a gas boiler.

I always find the surcharge cheeky. Both for KfW55 and for the air-to-water heat pump.

For KfW55, a better envelope is required. That means better insulation. And here ONLY material can cause an extra cost. The work is already there anyway. Except for monolithic construction. Anyway, the general contractor can do it that way.

I find it super cheeky with the air-to-water heat pump. You no longer need a chimney or a gas connection. Maintenance is also eliminated as is the chimney sweep.
But the heating engineer must be able to handle the heat pump. Otherwise, it can get expensive.

Isn't it possible that KfW55 is achieved solely through the air-to-water heat pump with somewhat better insulation?

However, air-water heat pumps and insulation can be sufficient. Ventilation is not a must, unless proof is provided according to the reference procedure of [KFW].