It’s important to make sure there’s enough fresh air inside. However the typical home has 4 times more fresh air (air changes per hour) than we need for health and oxygen supply. Even if you block all gaps, fresh air will still enter your home when you open the doors and windows.
Generally speaking, a lack of ventilation in a home is usually noticed by damp or even mouldy conditions forming – if this happens in your home then we recommend seeking professional advice.
Please note, if you have an unflued gas heater, special care needs to be taken as they require a supply of fresh air to operate safely. Consult a professional before weather proofing.