Grow Room BTU / AC Sizing Calculator

Grow Room BTU / AC Sizing Calculator

Size your AC quickly and accurately. Enter your lights, gear, and people to get required BTU/hr and tons—then add +20% headroom for hot days. Prefer help? Talk to a Grow Expert.

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Grow Room BTU / AC Sizing

In Simple, enter lights, equipment, and people. Switch to Advanced to add ventilation intake, dehumidifier, CO₂ generator, and room overhead.

Tip: Watts × 3.41 = BTU/hr. Add +20% headroom for hot days and filter loading. 1 ton of cooling = 12,000 BTU/hr.
We’ll fill size & lights; you can tweak anything.
Adds % to total after summing sources
1 W ≈ 3.41 BTU/hr 1 ton AC = 12,000 BTU/hr
How to use this calculator (step-by-step)
  1. Choose a preset (optional) to prefill size and light watts.
  2. In Simple, enter Total light watts, Other equipment watts, and People.
  3. Switch to Advanced to add ventilation intake (CFM & ΔT), dehumidifier watts, CO₂ generator BTU/hr, and a Room overhead %.
  4. Click Calculate. Review the breakdown, Required BTU/hr, and the +20% target.
  5. Size your AC by the Target BTU/hr (convert to tons by dividing by 12,000), rounding up as needed.
Formulas: Lights/Equip/Dehu BTU/hr = Watts × 3.41. People ≈ 400 BTU/hr each. Ventilation BTU/hr = 1.08 × CFM × ΔT (°F). Total = sum of sources; Overhead Added = Total × overhead%. Target = (Total + Overhead) × 1.20. Tons = BTU/hr ÷ 12,000.

Frequently Asked Questions

How do I convert watts to BTU/hr?

Multiply watts by 3.41. Example: 1000 W ≈ 3,410 BTU/hr.

How much heat do people add?

Plan about 400 BTU/hr per person of sensible heat during lights-on activity.

Do dehumidifiers and CO₂ generators add heat?

Yes. Dehumidifiers’ electrical watts convert to room heat (×3.41). Gas CO₂ generators list BTU/hr directly—enter that value.

How do I account for ventilation intake?

Use 1.08 × CFM × ΔT (°F) to estimate intake heat load. ΔT is how much warmer the incoming air is vs your room target.

Why do you recommend +20% headroom?

It protects you on hot days, filter loading, and minor mis-estimates so your system doesn’t run flat-out all day.

How do I pick tonnage?

Divide BTU/hr by 12,000. Round up to the nearest standard tonnage to avoid undersizing.

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