A caution I should have thought to include: if you do this to remove the carbon dioxide you exhale, you need to make sure you have enough ventilation that you don't asphyxiate. In the absence of carbon dioxide to tell you to seek fresh air, you won't notice the oxygen levels dropping; you'll just get stupid, then lose consciousness, then die. Homemade rebreathers have a high fatality rate. I don't think such good sealing is likely at the scale of an entire house unless it's literally underwater or something. But keep it in mind.