I often hear that ‘it used to be better’ – old houses were leaky, thanks to which the air was healthy and the walls ‘breathed’. Today’s construction is supposedly a tight ‘can’ in which a person suffocates.
As a man who has been in the industry since 1978, I will say briefly: this is nonsense that costs dearly.
Why exactly this air exchange?
Most think it’s just oxygen. Let’s count it. Lung capacity is 4–8 liters. With normal inhalation, we draw in about 0.5 – 1 liter of air. We take about 15 breaths per minute, which is about 900 liters per hour. So 1 m³ per person should be enough, right?
Nothing more wrong. When designing an installation, I assume values 20 times higher. Why? Because we have to change the air not only to breathe, but to ‘take out the rubbish’:
Chemistry: fumes from furniture, paints, clothes, and even from your phone or TV.
Moisture: with cooking, bathing and washing. If we do not remove it, we will live with the mushroom.
The standards are clear: we need a replacement of approx. 0.5 to 1 of the total volume of the house per hour. For the bathroom it is 50 m³, for the kitchen up to 70 m³. Each cubic meter must be heated in winter, and it costs money.
Leakage trap
Is an old, leaky house healthier? Why! In such a building, air exchange does not depend on your needs, but on the whim of the weather.
Windy Day: The exchange is gigantic. You lose a fortune on heating and the air becomes tragically dry.
Airless day: the exchange stops completely. You choke in your own fumes, even though the house is ‘holesome’.
Physics does not lie: how many ‘holes’ do you have in the wall?
To make you aware of the scale, let’s use the concept of an equivalent hole. Imagine one big hole in the wall through which the same amount of air escapes as through all the micro-sections in the house in the wind of approx. 30 km / h (Blowdoor test at 50 Pa).
Let’s take a house of 100 m² (250 m³ of volume):
Passive house (extreme tightness): has a ‘hole’ of 75 cm² (rectangle 7.5 x 10 cm). This is the height of our technological capabilities.
Standard New House: the standard allows for 5 times more airflow. This corresponds to a hole of almost 20 x 20 cm. Imagine that you have a wide open basement window throughout the winter. This is how we are building today!
Old House (without norms): This is where the drama begins. There are buildings where the air escapes as quickly as if there is a hole of 41 x 41 cm in the wall! Through such a hole, the thief will go inside without squeezing, and you are trying to heat it with your boiler.
Why do we need mechanical ventilation?
We build tightly not to suffocate, but to make it human, not the wind, to decide on the exchange of air. We put a lot of money in isolation and tightness tests, because uncontrolled airflow is a waste.
In the old buildings, all the heated air could ‘give’ out of the house in 3 minutes. Today, thanks to mechanical ventilation (recuperation), we can provide a comfortable 20 m³ per person without losing control of the wallet. Because knowing how to do it wisely is more valuable than the most expensive boiler in the basement.
