Houses with poor ventilation will have problems, but sealing buildings up is good for energy efficiency. "HRV" (heat recovery ventilators) are common and requi

Houses with poor ventilation will have problems, but sealing buildings up is good for energy efficiency. "HRV" (heat recovery ventilators) are common and required by code in many cold climates (Canada, northern Europe) which do whole-house ventilation with a heat exchanger so you're not just blowing all your nice warm air straight outside when it's -40C all week. The German Passivhaus standard shows what can be done with this approach, and it works very well.