I bought my parents a Netatmo weather setup. The one in the house measures temp, CO2 and the one outside temp, humidity. During Christmas Day visits with only

I bought my parents a Netatmo weather setup. The one in the house measures temp, CO2 and the one outside temp, humidity. During Christmas Day visits with only a half dozen people the room CO2 spiked to over 1,000ppm. Older house from the 1970s no HVAC. Opening a window (cross draft) brought it down to 300ppm. The room was stuffy before and great after so it shows how sensitive we humans are to air quality.