Indoor air quality: 7 warning signs in your home

We spend 90 % of our time indoors. Yet poorly ventilated indoor air is 2 to 5 times more polluted than outside air (WHO 2024). Here are 7 signs to watch for.

1. Condensation on windows every morning

If your windows run with water in the morning, air is not circulating enough. Overnight humidity (breath, sweat, plants) cannot escape, leading to mould and allergies.

2. Smells linger after cooking or showering

A clean extraction vent removes 90 % of smells in under 15 minutes. If smells linger over an hour, airflow is halved, usually clogged vents or ducts.

3. Allergies worse at home

If symptoms are worse at home than at the office, it’s rarely a coincidence. Mites, accumulated pollen, fungal spores, fine particles: poorly renewed air concentrates all these irritants.

4. Black spots in wall corners

Mould (Cladosporium, Aspergillus, Stachybotrys) appears when humidity stays above 65–70 %. They release mycotoxins breathed 24/7. Solution: effective ventilation + cause fix.

5. Dust returning too fast

If surfaces gather dust within 2–3 days, your air is particle-saturated. F7 / ePM1 70% MVHR filters capture 70 % of these, when they’re clean.

6. Fatigue or headache at home

Typical of excess CO₂ (> 1500 ppm). A closed bedroom for 2 can hit 2500 ppm in 6 hours without ventilation. Result: poor sleep, low focus, headaches.

7. The MVHR is silent… or too noisy

A silent MVHR probably extracts nothing. A noisy one is overloaded. Both extremes mean: time to inspect.

What to do if you recognise several signs?

1. Manually air rooms 10 minutes morning and evening, windows wide open.
2. Check vents are not obstructed.
3. Measure humidity with a basic hygrometer (40–60 % ideal).
4. Have your MVHR inspected if > 18 months without service.
5. Visible mould: intervene within 30 days.

The HUMINUS indoor-air audit

HUMINUS offers a full diagnostic: CO₂, VOC, humidity, PM2.5/PM10, MVHR inspection. Detailed report within 48h.