ᐅ Ventilation Concept for a Single-Family Home: Natural Ventilation, Air Leakage Devices (ALDs), Door Gaps – What Are Your Thoughts?

Hello everyone,

We are currently in the middle of a single-family house new build project and would like to get your independent opinion on our current ventilation concept. We are building with a general contractor, but are not always satisfied with the professional execution and explanation of some of the plans. Additionally, we have hired an external architect and have support from the Bauherren-Schutzbund – still, before the next step, we would like to get your assessment.

Construction of the house:
• Exterior wall: 17.5 cm (7 inches) sand-lime brick
• Mineral wool insulation according to KfW-40 standard
• Ventilated brick facade
• Two-story single-family house
• Living area: 200.2 m² (2,155 ft²)
• Air volume: 545.4 m³ (19,250 ft³)
• Building height: 6.4 m (21 ft)
• Average room height: 3.0 m (10 ft)
• High energy performance standard
• Low-wind area
• No windowless rooms
• Assumed n50 value: 1.0 h⁻¹ (only a reference value, not measured)

1. Ventilation concept result (according to DIN 1946-6)
According to the concept:

• Minimum air volume flow for moisture protection: 32.2 m³/h (19 CFM)
• Natural infiltration: 30 m³/h (18 CFM)

2. Proposed system
The planner chose the minimal possible solution:

• Pure natural ventilation
• Cross ventilation as a basis
• Outdoor air vents (OAVs) in the facade
• No fans
• No exhaust system according to DIN 18017-3
• No mechanical supply or exhaust air
• No heat recovery
• No duct or central system

3. Calculated air volume flows
For natural ventilation (for information):

• Moisture protection ventilation: 36 m³/h (21 CFM)
• Reduced ventilation: 126 m³/h (74 CFM)
• Nominal ventilation: 180 m³/h (106 CFM)

Pressure differences:
• OAVs: 2 Pa (0.008 in. w.g.)
• Transfer elements: 0.5 Pa (0.002 in. w.g.)

4. Room-specific air volumes / OAVs
All data from the table (source: page 5 of the PDF):

Supply rooms (each with 1 OAV):
• Guest room (14.5 m² (156 ft²)): 8 m³/h (5 CFM)
• Child room 2 (15.2 m² (164 ft²)): 10 m³/h (6 CFM)
• Bedroom (14.4 m² (155 ft²)): 10 m³/h (6 CFM)
• Child room 1 (15.3 m² (165 ft²)): 10 m³/h (6 CFM)
• Living/Dining/Kitchen/Hall/Gallery (97.4 m² (1,048 ft²)): 10 m³/h (6 CFM)

Exhaust rooms (also with OAV, each 1):
• Bathroom (13.3 m² (143 ft²)): 8 m³/h (5 CFM)
• Utility room (15.1 m² (163 ft²)): 8 m³/h (5 CFM)
• Toilet (5.1 m² (55 ft²)): 8 m³/h (5 CFM)

Total OAVs:
• Supply rooms: 5
• Exhaust rooms: 3

Note: The assigned 1 m³/h (0.6 CFM) per OAV are standard values – actual OAVs range between 10–40 m³/h (6–24 CFM).

5. Transfer air (quote: page 6 of the PDF)
Required transfer air volumes:

• Bathroom: 16 m³/h (9 CFM)
• Toilet: 16 m³/h (9 CFM)
• Utility room: 16 m³/h (9 CFM)
• Child room 1: 10 m³/h (6 CFM)
• Child room 2: 10 m³/h (6 CFM)
• Bedroom: 10 m³/h (6 CFM)
• Guest room: 8 m³/h (5 CFM)

6. Our concerns

• Cross ventilation is hardly reliably achievable in daily life (security, noise, winter operation, children’s rooms, etc.).
• OAVs can cause drafts, noise transfer, and heat losses.
• With KfW-40 standard + mineral wool + brick cladding + sand-lime brick wall, the house is extremely airtight – the n50 value of 1.0 is unrealistically high.
→ Actual airtightness = even lower natural infiltration.
→ The concept becomes even more fragile.
• High transfer air volumes lead to sound and privacy issues.
• The entire system completely depends on user behavior; mechanical support is entirely missing.
• The concept complies with the standard but does not meet the current state of the art for a KfW-40 new build.

7. Questions for the forum – what would you do?

• Is pure natural ventilation (windows + OAVs) still recommended for today’s very airtight new builds?
• How do you assess the high transfer air volumes – are they practical or rather problematic?
• Would you recommend a mechanical system (exhaust system, decentralized ventilation, or controlled residential ventilation with heat recovery)?
• Is it normal that a general contractor only provides the absolute minimal concept?
• Should a mechanical ventilation system be mandatory in KfW-40 construction?
• Would you have the general contractor revise the concept or commission a completely external design?
• What would you do next if you were in our position?

I am very much looking forward to your assessments – thank you very much for your support!

Best regards

Simple answer (applies to every new build, since all houses today are airtight):

1. Central mechanical ventilation with heat recovery
2. Decentralized mechanical ventilation with heat recovery, if the budget doesn’t cover option 1

For me, comfort and air quality alone are undeniable.

You can try to justify everything with manual ventilation and calculations, but you have to be honest with yourself that you’re only fooling yourself.

You are the client. So order mechanical ventilation with heat recovery. End of discussion -;)

I approached this very practically. I bought an air quality monitor to check how often I need to ventilate. Even in my current old building, it’s several times a day to keep the CO2 levels below 1200 ppm.
In any case, my new build will have a central ventilation system. If you install it yourself, the cost is around 6000–8000€ (approximately $6,400–8,500). It’s very easy to do yourself (anyone who has one and has watched the installation can confirm that).

Sonar87 schrieb:

Is it normal that a general contractor only provides the absolute minimum concept?

You get what is stated in the scope of work or what has been specifically commissioned. If nothing has been agreed upon and the scope of work does not specify anything particular, then you get the minimal solution.

I also support the team: centralized controlled residential ventilation!

Sonar87 schrieb:

Is it normal for a general contractor to deliver only the absolute minimum concept?

Yes. If someone offers a low price, you usually get only the essentials.
For some, this is sufficient because they can ensure manual ventilation, whether due to a compact house size or available time and patience.

Sonar87 schrieb:

Would you recommend a mechanical system (exhaust system, decentralized ventilation, controlled residential ventilation with heat recovery)?

Yes

Sonar87 schrieb:

Is natural ventilation alone (windows + air inlet devices) still advisable in today’s very airtight new buildings?

No, unless you don’t care about comfort and can reliably manage manual ventilation. Otherwise, the house will have a defect when it comes to resale value.

This is your answer regarding controlled residential ventilation

Sonar87 schrieb:

Cross-ventilation is hardly reliably possible in everyday life (security, noise, winter operation, children’s rooms, etc.).

And to put it bluntly: if you want to afford a 200 sqm (2,150 sq ft) house, you should also invest in the necessary technology.

Hello everyone,

Thank you very much for the feedback and your assessments so far — it has already been very helpful to us.

We would like to ask a few more questions:

• Which specific brands or models of centralized ventilation systems can you recommend? What are the key aspects to consider when choosing one (efficiency, heat recovery, noise levels, operation, maintenance, etc.)?
• Additionally, we are considering having an external air conditioning system installed due to the large panoramic windows and possible overheating during summer. Do you have experience with combining ventilation and air conditioning, and can you recommend effective systems or approaches?

For comparison: Our general contractor estimated around €16,000 (approximately $17,000) for a centralized ventilation system including installation.

Thank you and best regards