The windows all still open, but in winter we have (nearly) enough MHRV (Mechanical Heat Recovery Ventilation) not to need to ventilate directly, eg see: https:

The windows all still open, but in winter we have (nearly) enough MHRV (Mechanical Heat Recovery Ventilation) not to need to ventilate directly, eg see: https://www.earth.org.uk/MHRV-mechanical-heat-recovery-ventilation.html https://www.earth.org.uk/MHRV-mechanical-heat-recovery-venti...