Hi everyone,
I wanted to share a small Home Assistant project I built for my indoor grow tent.
My first version used simple RH/temperature rules: fan on when humidity was high, humidifier on when humidity was low, light on a schedule. It worked, but RH alone quickly became misleading. The same 60% RH can mean very different things depending on temperature, especially when the grow light turns on/off.
So I rebuilt the logic around VPD instead.
The setup uses normal Home Assistant entities:
- temp/RH sensors as
sensor.* - fan, humidifier, light and optional heater as
switch.*
No custom integration or special hardware.
The control loop checks the climate every 15 seconds and roughly works like this:
temp/RH sensors ā averaged readings ā VPD ā day/night targets ā safety checks ā fan/humidifier/heater decision
The hardest part was not calculating VPD. It was making the automation behave safely when things go wrong: sensor failures, critical humidity, heater runtime, Home Assistant restarts, cyclic ventilation, and the fan/humidifier fighting each other.
I also built a Lovelace dashboard with Setup, Grow, Settings and Diagnostics views.
Here is the Grow dashboard from my setup:
I also made a simple VPD calculator here if anyone wants to sanity-check temp/RH values:
Happy to answer technical questions. Iām also curious if anyone here has built similar climate logic for grow tents, greenhouses, terrariums, fermentation chambers or other controlled environments.