ᐅ Decentralized exhaust ventilation system without heat recovery in KFW 40 new construction
Created on: 28 Sep 2025 17:58
C
Cloud87
Hello,
we have the option to install a decentralized ventilation system in our 1.5-story new build (124 sqm (1,334 sq ft)) through the builder. The KfW loan has already been approved. We have now been informed that we could also do without the ventilation system and save €1,300 by relying on conventional (intermittent) ventilation instead.
The exhaust system would work by creating an opening in the exterior wall in the bathroom, guest toilet, kitchen, and utility room, through which a fan would expel the air outside. In the living/dining area, office, and bedrooms, seals on the windows would be removed to allow fresh air to enter.
We are torn because we are concerned about mold on one hand, but on the other hand, we do not want noise or disturbing thermal bridges as a result. What would you recommend?
A heat recovery system is unfortunately not an option for us due to the costs.
Thank you in advance
we have the option to install a decentralized ventilation system in our 1.5-story new build (124 sqm (1,334 sq ft)) through the builder. The KfW loan has already been approved. We have now been informed that we could also do without the ventilation system and save €1,300 by relying on conventional (intermittent) ventilation instead.
The exhaust system would work by creating an opening in the exterior wall in the bathroom, guest toilet, kitchen, and utility room, through which a fan would expel the air outside. In the living/dining area, office, and bedrooms, seals on the windows would be removed to allow fresh air to enter.
We are torn because we are concerned about mold on one hand, but on the other hand, we do not want noise or disturbing thermal bridges as a result. What would you recommend?
A heat recovery system is unfortunately not an option for us due to the costs.
Thank you in advance
B
Bierwächter29 Sep 2025 20:04I would seriously reconsider that. Our current build is costing so much more than planned that our contingency fund is gone, and we might even have to borrow from our parents. This is despite giving up on a garage, carport, and photovoltaic battery.
However, the central ventilation system is one of the main reasons we’re excited about the house. Manual ventilation is a nightmare for us. I’d rather do without a kitchen and cook on a portable hotplate for a year.
I also can’t imagine getting KfW40 certification with any air leakage.
However, the central ventilation system is one of the main reasons we’re excited about the house. Manual ventilation is a nightmare for us. I’d rather do without a kitchen and cook on a portable hotplate for a year.
I also can’t imagine getting KfW40 certification with any air leakage.
For KfW 40 standard, heat recovery is practically mandatory. Window rebate or forced ventilation often compromises both energy efficiency and sound insulation and does not provide filtration. Centralized controlled residential ventilation or decentralized room-by-room heat recovery systems are better; they comply with DIN 1946-6 and improve comfort. In brick construction, there are discreet, system-integrated facade solutions (e.g., from Leipfinger-Bader).
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