ᐅ Decentralized exhaust ventilation system without heat recovery in KFW 40 new construction

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

What does the KfW application/proof state? What does the ventilation concept according to DIN say?

What does the energy consultant, who has to conduct the BnD, say? And finally: really a developer?

Great, that’s like having constantly open windows. It was common back in the 1940s.
Not having any (central or decentralized) mechanical ventilation with heat recovery in a new building is comparable to buying a new CRT TV. You can do it—but generally, no one wants to because there are only disadvantages.

In new construction, people usually choose:
1. Central mechanical ventilation with heat recovery
2. Decentralized mechanical ventilation with heat recovery, if the budget is tight
3. Window-frame ventilation, if you really can’t afford the house but are building anyway (no offense intended)

Hi
I wouldn’t bother with mechanical exhaust ventilation. If you want to keep the heat out or the smell from the neighbor’s barbecue, you don’t stand a chance.
Controlled ventilation is fine, but if that’s not possible, then manual ventilation.
PS: You can always retrofit mechanical exhaust ventilation using window frame vents for little money if needed – but it’s still not great...
Gerddieter

Gerddieter schrieb:

Hi
I wouldn’t want to deal with forced ventilation. If you want to keep the heat outside or avoid odors when the neighbor is grilling, you don’t stand a chance.
Controlled ventilation, definitely; if that’s not possible, then manual ventilation.
PS Forced ventilation through window frame vents can be added anytime at low cost if needed – but it’s still not great...
GD

PS: As a landlord, I would install forced ventilation.

Cloud87 schrieb:

We have now received information that we could also do without the ventilation system and save €1,300 (about $1,430).

P.S. That is the savings for two decentralized units. So basically no discount for a whole-house ventilation system.
I would also be interested in the calculation for achieving the KfW standard. After all, KfW 40 (!!!), where building with window-frame vents completely ruins the entire calculation. Are you really spending such a fortune on a very high-quality house that it ultimately comes down to just €1,300 (about $1,430)? I can think of many things I could do without—buying a modern used property without a ventilation system is like buying a new car with a big scratch. Also keep in mind that you may want to sell the property at some point. Or would you still buy single-pane glazing today?