Chimney no longer allowed from 01.04.16 in KFW 55?

But it does not say that a [Kamin] is prohibited!!!

If the "Alternative verification method according to reference values" is to be used, the annex states:

"Additional heat generators for heating or domestic hot water are not permitted, not even as supplementary heat generators."

When applying the classical verification method, the annex notes:

"If a central heating system is present, manually fed individual stoves that are not integrated into the circulation system cannot be taken into account. For central heating systems with integrated biomass-fed individual stoves as well as automatically fed pellet primary stoves, a maximum coverage share of 10% of the useful energy demand can be assumed."

I told you, a fireplace is not forbidden - that's what it says there too.

I told you, a fireplace is not forbidden - that's also what it says there.

Definitely. A fireplace does not necessarily have to be a (creditable) heat generator, but can also be installed just "for the eye"/feeling.

That means forbidden according to the reference value, allowed in the classical way?

What kind of reference value? it is allowed but is not included in the calculation if it is not water-bearing or the wood supply (pellets) is automated.

So if you want to have one, then you are allowed to build it, even after 1.04, that was your question, wasn't it, or do you want to know something else.