"Normal" is gonna range between 300-600 ppm in an enclosed structure occupied by mammals. Much higher when the same enclosed space is occupied by mushrooms.
rhizome Reviewed by rhizome on . What's "normal" CO2 PPM for a closed-up house? If my grow closet is recirculating air from the house, what CO2 concentration is "normal" for a closed-up house (the house is not vented: windows are closed, and using a central air conditioner). Perhaps some folks who have CO2 monitor/controllers have walked around their house and taken measurements. Could CO2 concentrations in a closed-up house rise above the "safe" maximum of 2500 PPM? Almost a year ago, extinctx11 posted a similar question (but got no responses): Rating: 5