The really old buildings obviously had no ventilation other than simply being not-very-sealed. Only a couple of generations ago there were still houses with sin

The really old buildings obviously had no ventilation other than simply being not-very-sealed. Only a couple of generations ago there were still houses with single glass windows, there weren’t any moisture barrier film in the building shell, doors weren’t well sealed and so on. The second gen with forced exhaust emulates the old self-draft by forced exhaust ventilation and that exhaust air has to be replaced by air that enters somewhere and since the air is evacuated from kitchen/baths it’s let in through all other rooms. Yes that air can be cold/dry and it’s also uneconomic if it’s -20C so these vents are adjustable so you can close them somewhat when needed. Heat exchanged air forces both from and to the building is of course an improvement over the from-only, but the ductwork required is much more complex so it’s mostly done in new builds. The great thing about forced exhaust only is if it’s combined with a heat pump that reclaims the heat so it’s not wasted. As far as I know the rule of Thumb regardless of system is that all the air in the house should be replaced every two hours using only the base flow i.e excluding the kitchen fan. So air quality is ensured for both systems as they shift the same volume of air, but comfort and economics is better with the more expensive system (no freezing fresh air entering).