Hello Ben,
The central ventilation system is unfortunately too expensive for us. Our general contractor wants nearly €9,000 for it. With the decentralized solution, we are at about one third of that. Additionally, we are afraid of germs, compromises in sound insulation, etc. Added to that is the space requirement in the utility room.
The fear of "germs" is artificially stoked to give insecure builders an argument to dispense with "supposedly" more expensive devices; usually a common tactic of poor salespeople.
The issue of sound is rather a problem with decentralized systems, which is also logical, because you have to accept outlets in your well-insulated exterior wall. Someone should really put an article on our website about this topic soon.
Our "planner" so far was "only" the very knowledgeable sales advisor. He expects us to achieve KFW70 with this house, but also says that the structural engineer has to calculate that. I definitely consider that serious. But: My fear is that after signing the contract the €5,000 solar system will be added.
Finally a good example of serious sales advice; at least I hope so.
Maybe someone has so much experience that they can give hope of KFW70 based on my data?!
No one can say that reliably, if it were possible, €uro – whose area of expertise your question concerns – would have answered differently.
It depends on the location of the property, the components used in the house construction, the total heat demand of the new building and much more. I am currently also facing the problem of realizing a KfW 70 efficiency house in which a gas condensing boiler is to be used as the heat generator. At this point:
Thanks €uro for your help
From experience with other building projects, I know that KfW 70 can be achieved almost everywhere – perhaps with one or two additional options (depending on the aforementioned circumstances) – where an air-to-water heat pump is used. Which brings me back to your opening sentence. If ventilation is planned anyway, you can generally use combination units if only one party is going to live in the new house; for rented portions each apartment should be supplied independently. These do not take up much more space in the utility room than a standard gas/condensing boiler with fittings, expansion vessel and storage tank; thereby you can also do without the – disliked by most HVAC planners – solar system.
If I understood your post correctly, this would mean for you: You give up the decentralized ventilation for about €3,000 and the gas/condensing boiler for about €3-4,000 depending on provider and size, and in return you receive a credit. The surcharge – then for the combination unit – should in my opinion be moderate and offers the great advantage that it contains an air-to-water heat pump as well as controlled residential ventilation with heat recovery, and you do not have to accept a loss of space in the utility room; you also save the often not insignificant costs of the gas connection.
But: My fear is that after signing the contract the €5,000 solar system will be added.
This sentence actually worries me more. I was pleased at first about the salesperson you praised. But has he also fully informed you about the expected additional construction costs? If you have taken these costs into account in your financing plus costs for painting/flooring work and outdoor facilities as well as an amount "X" for extras, €5,000 should not really scare you.
Addition:
Poorly maintained air conditioning and ventilation systems pose an acute health risk. Delayed filter changes, dirty air ducts or germ-contaminated humidifiers promote the growth of dangerous pathogens that can cause life-threatening lung diseases in humans.
A common mistake is exchanging the filters of ventilation systems too late. If the drawn-in air passes through overloaded filters, the systems blow more pollutants into indoor spaces than they filter out. If bacterial and fungal colonies have already formed, the dangerous germs can spread throughout the entire building and settle, for example, in kitchens.
The fine fins of coolers and heaters in air conditioning systems and the many meters of ventilation ducts must also be regularly cleaned and inspected for dirt and moisture areas. This is often made more difficult by the absence of inspection openings,
a case of classical planning error.
The most serious defects occur with humidifiers, because stagnant water between 25 and 45 degrees Celsius forms an ideal breeding ground for bacteria, especially the dangerous Legionella. In systems with humidifiers, therefore, continuous water replacement must be ensured.
The relevant VDI guideline 6022 on “Hygiene requirements for ventilation and air conditioning systems and devices” requires such systems to be regularly checked for contamination and moisture paths and, if necessary, cleaned by qualified specialists. In systems with humidifiers, this is required every two years, without humidifiers every three years.
Kind regards