Does my HVAC need to be on for RH testing to be accurate? Do I need to document these ambient conditions and why?

In order to meet the ASTM F2170 standard, the concrete slab and the occupied air space above the slab must be at service conditions for a minimum of 48 hours prior to testing and for the entire 24 hours while the test is conducted. However, even not considering the ASTM standard, it’s a best business practice to have the slab at service conditions before testing. Ambient conditions play a key role in the drying time of a concrete slab, and any change to those conditions will affect the moisture movement through the slab and will change the internal RH. Testing at non-service conditions can become a pointless exercise if drastic changes to the environment will ultimately skew the test results and, ultimately, slow the drying process.