Returning home: vacation recovery

A home with no occupants for 5 or more days has a characteristic settled state: CO₂ at outdoor baseline (around 420 ppm), VOCs decayed from peak by a factor of 2-10 depending on source surface area, humidity drifted toward outdoor equilibrium through envelope exchange, PM_2.5 at the outdoor baseline minus infiltration losses. That settled state is the cleanest the air gets in a normal household.

On return, treat the first 24 hours as a diagnostic window and follow each room's readings in the app or web dashboard. CO₂ rebounds within hours of occupancy resuming; if it climbs unusually fast, the ventilation has degraded since you left (filter clogged, fan failed, HRV stopped). VOC may rebound from settled surfaces as temperature rises (HVAC was set back during absence, returns to setpoint, off-gassing accelerates). Humidity climbs with occupancy (cooking, showers, breathing) and the speed of the climb tracks the household activity level.

Any parameter that is meaningfully different from your pre-vacation baseline is worth investigating. A higher post-vacation humidity baseline (when the home was sealed and warm) sometimes reveals a hidden moisture source: a slow plumbing leak, a basement water intrusion, a dehumidifier failure. A higher post-vacation VOC baseline sometimes reveals a slow off-gassing source you had habituated to (a piece of furniture, a finish, an air-freshener device). The vacation gap acts as an unintentional baseline reset.

For households that vacation regularly, comparing trips can be revealing. Terrestream does not compare trips for you, so each time you come back, note where VOC and humidity settled while the house was empty; the 7-day and 30-day charts in the app show the days before you returned. A slowly-rising post-vacation VOC floor over a year is consistent with a gradually-degrading material somewhere in the home. A slowly-rising humidity floor is consistent with a moisture-control issue that needs investigation before it produces a mold event. Most vacations are uneventful in the data; the ones that are not are usually pointing at something real.