I can see that might being confusing if you are not used to it, but houses are build to be “as airtight as practically posible” of course you could never bild a normal hous as airtight as a spaceship, but if you look at windows doors etc of a passive house you’d see rubber gaskets and seals everywhere. New tech keeps coming up. All houses since early 2000 here are required to have an inner airtight membrane and there are strict requirements about how to apply it. All seams, corners and nail holes etc. must be taped with special membrane tape. In theory the only holes in the house should be the ventilation system. I’m my current apartment even the kitchen hood is connected to the ventilation system so when it runs and an even amount of air is being exhausted and injected back into the house to avoid any pressure differential, minimizing leaks from the inevitable tiny leaks here and there. Airtight is the goal and we are damn close. Many houses are also better than the standards to account for small leaks over time.
Edit and additional: you are of course allowed to have passive airvents to the outside and you can always open windows and doors to allow for natural ventilation but when they are close they are airtight and in winter when it’s cold you should definitely close ALL of them and rely on the mechanical ventilation. Leaks are a huge heat loss, but in summer you open it up at night to allow for cooling, but as I said, in my country at the moment those cooling methods are poorly implemented still.
I can see that might being confusing if you are not used to it, but houses are build to be “as airtight as practically posible” of course you could never bild a normal hous as airtight as a spaceship, but if you look at windows doors etc of a passive house you’d see rubber gaskets and seals everywhere. New tech keeps coming up. All houses since early 2000 here are required to have an inner airtight membrane and there are strict requirements about how to apply it. All seams, corners and nail holes etc. must be taped with special membrane tape. In theory the only holes in the house should be the ventilation system. I’m my current apartment even the kitchen hood is connected to the ventilation system so when it runs and an even amount of air is being exhausted and injected back into the house to avoid any pressure differential, minimizing leaks from the inevitable tiny leaks here and there. Airtight is the goal and we are damn close. Many houses are also better than the standards to account for small leaks over time.
Edit and additional: you are of course allowed to have passive airvents to the outside and you can always open windows and doors to allow for natural ventilation but when they are close they are airtight and in winter when it’s cold you should definitely close ALL of them and rely on the mechanical ventilation. Leaks are a huge heat loss, but in summer you open it up at night to allow for cooling, but as I said, in my country at the moment those cooling methods are poorly implemented still.