diff --git a/esphome/fdm-exhaust-fan-control.yaml b/esphome/fdm-exhaust-fan-control.yaml
index 2b6adc1..6b22d22 100644
--- a/esphome/fdm-exhaust-fan-control.yaml
+++ b/esphome/fdm-exhaust-fan-control.yaml
@@ -36,13 +36,20 @@ web_server:
   port: 80
 
 # GPIO Outputs for fan control
+# IMPORTANT: inverted: true because NPN transistor driver inverts the logic
+#   GPIO HIGH -> NPN ON -> Gate LOW -> Fan OFF
+#   GPIO LOW  -> NPN OFF -> Gate HIGH (5V via pull-up) -> Fan ON
 output:
   - platform: gpio
-    pin: GPIO3  # D1 on XIAO
+    pin:
+      number: GPIO3  # D1 on XIAO
+      inverted: true
     id: fan_80mm_output
 
   - platform: gpio
-    pin: GPIO4  # D2 on XIAO
+    pin:
+      number: GPIO4  # D2 on XIAO
+      inverted: true
     id: fan_120mm_output
 
 # Fan entities for Home Assistant