Open your windows:
Before & After CO2
https://blossom.primal.net/b22c6917fc9f477a970c1432eb169712629df13ef1ab8f35311f88de31ba0bfd.jpg
https://blossom.primal.net/1e21cbffaff3a00e35ced718fefcb45e309159...
You can add an ERV or HRV depending on your climate to your furnace