This has been posted on other forums, but I didn’t have personal experience until now. I have several of the 4-in-1 sensors, so I have multiple humidity readings throughout my home. The NEST humidity reading was consistently LOWER by about 10-15 percent.
I attributed it to the NEST thermostat, I mean how accurate could it be? And, I didn’t much trust the 4-in-1 humidity readings, I would just pick one for a trigger device, and turn on and off my humidifiers based on that. If I wanted my house to be 50%, set the trigger to 40%… you get the idea.
On another forum, they recommended caulking(?) the hole behind the NEST thermostat. I had nothing to lose, so why not? I used that pink wall putty stuff (the thermostat is not going anywhere) and carefully filled the hole in the wall behind the base plate. I was careful to avoid the connections especially the connector that snaps into the unit itself. I snapped the NEST back on to the wall plate.
I checked my Vera3. WHA? The Vera humidity ready is now within a couple points of the 4-in-1 readings! The WWN humidity sensor jumped immediately to match my 4-in-1 readings. Very cool. I now trigger my humidifiers based on the WWN humidity reading, and have some confidence in the accuracy (well ±5%).