The saying is to seal it tight and ventilate it right and that does sound confusing. But, you are addressing two different issues, energy efficiency and air quality.
From an efficiency point of view, air leakage not only transports your expensive energy to the outside, it reduces the efficiency of the insulation it often passes through. Old homes certainly provided enough fresh air, but they were far from energy efficient.
However, once we tighten up the house beyond a certain point we can encounter air quality issues, thus they recommend mechanical ventilation or at the least cracking open a window (not very reliable).
So, what is the benefit of air sealing if we have to turn around and add ventilation? It boils down to the path the air takes. Much of the air one breathes in an old leaky house comes from the basement or a crawlspace, not the best source of air to breathe. It also filters through old insulation that has become contaminated with dust, pollen, and other pollutants from outside and maybe some rodent droppings from inside.
If you want the benefits of fresh air, seal the undesirable leaks and provide nice clean serviceable air paths for incoming air. In reality, houses don't need to breathe, it is the people inside that need the good air.
Bud
