📊 The Definition
The n50 index tells us exactly how many times the total air volume of the home changes in one hour, under this 50 Pa pressure.
The n50 Directive: What Are the Limits for Passive Houses (Passivhaus)?
A Passive House is not simply a "well-insulated" home. It is an international, strict scientific construction standard (originating from Germany) that promises to reduce energy consumption for heating and cooling by up to 90% compared to conventional buildings.
To achieve this extraordinary saving, the heart of the home is the mechanical ventilation system (MVHR) we examined. But for MVHR to work, the home must be an absolutely sealed box. This is where the famous n50 index enters the picture.
1. What Does n50 Mean?
As we saw in the Blower Door Test article, the fan creates an artificial pressure difference of 50 Pascals (Pa) between inside and outside (this simulates roughly a strong wind of 30-40 km/h hitting the home from all sides).
2. The 'Golden Limit' of 0.6
For a home to be certified as a Passive House by the Passivhaus Institute, the rule is one and non-negotiable: The n50 index must be less than or equal to 0.6.
🏚️ Old Home (pre-1980)
The n50 can be from 10.0 to 15.0 (leaky as Swiss cheese).
🏠 Modern New-Build
According to regulations, it is considered "good" if it achieves an n50 of around 3.0.
🏡 Passive House
Below 0.6. We are talking about a construction that is 5 times more airtight than a brand-new, "good" conventional home!
📐 What does this mean in practice? It means that even when the home is "battered" by strong winds, less than 60% of its air is allowed to leak outward in one hour!
3. Why 0.6 Is Not Just a 'Fetish'
If the n50 is, for example, 1.5, the MVHR system begins to lose its purpose.
🌬️ The Easy Path
Air prefers to exit and enter through the gaps (the "easy" path) rather than pass through the filters and heat exchanger of the machine.
💸 Lost Savings
So you lose heat through the holes, the machine runs pointlessly and the promise of "zero consumption" goes up in smoke. 0.6 is the scientific threshold beyond which mechanical heat recovery becomes absolutely dominant!
4. The 10x10 Model Experiment (The Final Exam)
The contractor promises he has built us a "Passive House" of 100 sq.m. The official inspector arrives with the Blower Door for the final certification.
❌ Scenario A (Failure - n50 = 1.2)
The fan sucks. The screen reads 1.2. The home is excellent by Greek standards (very warm), but failed the Passivhaus exams. The inspector deploys smoke and discovers that the electrician did not seal the main conduits at the distribution board, and the plumber left a gap around the drain. Certification is cancelled until the points are dismantled and properly sealed!
✅ Scenario B (Absolute Success - n50 = 0.4)
The screen reads 0.4! The home is more sealed than a space station. The certificate is issued. The heat pump (now a tiny device) consumes as much electricity as… a hair dryer to keep the entire home at 22°C through the harshest winter!
The Final Conclusion: The n50 ≤ 0.6 directive is the "Holy Grail" of modern construction. It completely changes the way we build. The builder can no longer say "don't worry" about a small gap, because the machine will ultimately "catch" him. Construction quality is no longer judged by the eye, but proven by the numbers!
Related Articles
Blower Door Test: How it measures the 'holes' in your home How airtightness boosts heat pump efficiency by 20% Mechanical Ventilation with Heat Recovery (MVHR) Sealing air leaks: Silicones, foams, specialised tapes
Ventilation, Airtightness & Real Consumption: Climate Control
Return to category.
Go to categoryCentral Guide
Return to the central guide.
Go to guide