A first question in response to a home CO2 reading might be about its health implications. This issue is addressed by Usha Satish et al. in their 2012 paper
Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance 
The writers point out that it has been thought that adverse effects attributed to raised CO2 levels in the home are actually due to other pollutants commonly associated with CO2. They describe how their experiment was designed to eliminate this possibility and so isolate the effects of CO2.
Before presenting their own findings, they summarise previous research on levels of CO2 much higher than those likely to be encountered in the home: “CO2 concentrations > 20,000 ppm cause deepened breathing; 40,000 ppm increases respiration markedly; 100,000 ppm causes…