Prefabricated house, gas condensing boiler vs air-to-water heat pump - which energy efficiency, advice?

Hello forum members,

I am reading here with great interest and have already learned a lot. Thank you very much!

We are currently planning the construction of a house and have been going around in circles with the architect for weeks.

It is to be a prefabricated house without a basement. The west gable is to have large window areas, but energy efficiency is also important to us. Our architect is pushing us towards an air-water heat pump but cannot give a solid reason for it.

She says it is possible:

KfW 70

[*]with gas condensing boiler + solar + cross heat exchanger or air-water heat pump with cross heat exchanger with large window front and without under-slab insulation;

KFW 55

[*]only with air-water heat pump with cross heat exchanger as well as partial window reduction and under-slab insulation.

At the moment, I only have the standard offers for the respective technologies, the standard construction description, and the cubature.

Now the heating engineer has called me as an expert. His interest is probably only to push me towards a high investment, right?

Which documents do I need in order to hire an independent consultant and what should I look out for when searching for this consultant?

I have heard enough flowery sales pitches in the conversations, I would like to support the whole thing with data and facts.

Thank you very much for your help!
BS

Hello,

.... Our architect is pushing us towards an air-to-water heat pump, but she cannot provide a solid reason for it...

She is probably not trained for that either. It is surprising that she is "putting herself out there" so much. If you have or represent an opinion, you should be able to support it with concrete facts and figures => basic determination.

....
She thinks it is possible:

KfW 70

[*]with gas condensing boiler + solar + cross heat exchanger or air-to-water heat pump with heat recovery ventilation with a large window front and without insulation under the floor slabs;

KfW 55

[*]only with air-to-water heat pump with heat recovery ventilation as well as partial window relinquishment and insulation under the floor slabs.

[*]That would be questionable ;-)

....As an expert, the heating engineer has now called me. His interest is probably only to push me towards a high investment, right?

Not only that, it also matters how he can handle modern technology. However, you cannot accuse him of primarily thinking about his own pocket. After all, he lives in our social system. With precise planning/dimensioning, you can steer his "scope for design" in the right direction ;-)

....Which documents do I need to hire an independent consultant ...

The measured floor plans and section(s) of all floors as *.pdf. Also helpful is the energy saving ordinance/KfW proof, if available, also as *.pdf or the definition of the intended, used components.

....and what should I pay attention to when looking for this consultant?

To independence from sales, i.e. objectivity. Clarify costs before awarding the contract.

...I have now heard enough flowery sales phrases in the discussions; I would like to underpin the whole thing with data and facts.

With independent planning with an architect, you are not subject to the restrictive conditions of a general contractor/general planner project. Almost all options are open to find an economic optimum.

regards

Hello,

Especially when it comes to heating, you should definitely consult an additional specialist besides the architect. This can be, as you mentioned, not only a heating engineer but also a building services planner who advises you as another independent expert. If you decide to go with the advice of a heating engineer, you should definitely obtain several different offers. Regarding achieving the energy efficiency classes, you should definitely be given more explanation than you have currently provided, especially if your architect does not have any real arguments for it. You should ask her again to what extent she has a professional background in building services or whether it would not be better to involve a specialist planner for this area.

A statement about your possibilities for achieving the energy efficiency classes without knowing the exact plans and the system is not possible as a remote diagnosis. You should really consult a specialist if the architect cannot provide clear information.
Regarding the heating engineer himself: of course, he always has entrepreneurial thinking in mind, but he will also care about your satisfaction and make sure that he actually gets the contract. So you can certainly get an overview of the market by comparing different heating engineers.
As documents for a building services planner, you need the plans, and if your architect has already calculated something regarding energy efficiency or energy consumption, you will need those documents as well.
When choosing a specialist planner, you should apply the same evaluation criteria as when selecting your architect. Certainly important are the expertise, which can be assessed based on references, the costs, and what kind of consulting and planning scope is offered to you, and of course, very much also your feeling that you get during the conversations with the specialist planner.

Best regards