Am I being stupid

Hey That's an excellent question that gets to the heart of managing VPD (Vapor Pressure Deficit). This temperature drop phenomenon is completely normal: it's what we call evaporative cooling (the same principle as sweating that cools us down). Here’s how I would handle it to keep a stable environment: 1. Don’t correct the temperature immediately The temperature drop you’re observing is real, as energy (heat) is being used to turn liquid water into mist/steam. If you increase your heating to compensate, you risk creating brutal fluctuations as soon as the humidifier stops. My recommendation: Prioritize adjusting your target humidity first. Once the humidity is stable for an hour or two, check your temperature. 2. The sensor issue (The false reading) You’re right: if the mist hits your sensor directly, the reading is skewed and often much lower than the actual canopy temperature. Action: Move your sensor! It should be placed in the shade (under a leaf or in a small ventilated box) and especially opposite the humidifier’s output. It should measure the ambient air in the tent, not the steam jet. 3. Adjust according to the life stage If after moving the sensor, your temperature stays below 21-22°C, then yes, slightly increase your heating or lower the extraction. At 24°C, you’re in an ideal comfort zone. If it drops to 21°C with humidity, that’s still very acceptable for most phases, especially if you’re under LED because plants like slightly warmer air to compensate for the lack of infrared heat on the leaves. 4. Use VPD as a guide Rather than setting a temperature or humidity, try aiming for a VPD target. If your temperature drops, your "relative" humidity naturally increases. Sometimes, letting the temperature drop a bit helps achieve the right balance without doing anything else. In summary: Don’t chase the numbers. Move your sensor away from the mist, stabilize your humidity, and only if the temperature falls below 20°C, turn up your heating. Wishing you a good evening!