Question 1

What is VPD and why does it matter for my grow room?

Accepted Answer

VPD (Vapor Pressure Deficit) measures the drying power of the air around your plants. It controls how fast plants transpire — pulling water and nutrients from roots to leaves. Optimal VPD ranges are 0.8-1.2 kPa for vegetative growth and 1.2-1.6 kPa for flowering.

Question 2

How many BTU do I need to cool my grow room?

Accepted Answer

A common rule of thumb is 3-4 BTU per watt of lighting, but the true answer depends on all heat sources: lights, dehumidifiers, CO2 burners, people, and insulation quality. Our calculator accounts for all of these.

Question 3

Is the VPD calculator free?

Accepted Answer

Yes. The VPD calculator with interactive heatmap and BTU cooling calculator are completely free. The full suite (dehumidification, ventilation, CO2, electricity costs, light planner, grow cycle, and downloadable Environment Plan) is a one-time purchase of $14.99.