I also have a CO2 meter, and it's not hard at all to get above 1500. 5000+ is where you start getting concerned, but the air is noticeably stuffy way before tha

I also have a CO2 meter, and it's not hard at all to get above 1500. 5000+ is where you start getting concerned, but the air is noticeably stuffy way before that with all the other organic compounds humans exhale.