Grow Room BTU / AC Sizing Calculator

Grow Room BTU / AC Sizing Calculator

Stop guessing — calculate the exact BTU and tonnage your grow room needs to stay cool. Enter your room size, lights, and equipment to get a tailored recommendation. Need help choosing? Talk to a Grow Expert.

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BTU / AC Sizing Calculator

Enter your room and light details for a quick result. Switch to Advanced to include equipment, people, and dehumidifier heat load.

How to use this calculator
  1. Enter room dimensions — length, width, and ceiling height in feet.
  2. Enter grow light wattage — use the actual draw from your driver label, not marketing specs.
  3. Select headroom — 20% is standard; use 30% for sealed rooms with CO₂.
  4. Advanced mode — add equipment watts, dehumidifier watts, number of people, and ventilation details for a complete heat load picture.
  5. Click Calculate BTU — see total BTU, tonnage, and a recommended AC unit size.
  6. Shop the right unit — find mini-splits and portable ACs sized for grow rooms.

Formula: BTU/hr = (Total watts × 3.41) + (People × 400) + Vent infiltration. 1 ton = 12,000 BTU/hr.

🍩 Heat Load Breakdown — Visual Donut Chart ▾
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BTU/hr
Calculate above to see heat load breakdown →

Each slice shows one heat source's share of your total BTU load. Lights are typically the dominant source at ~70–80%. Hover or tap a slice to see the exact value.

Grow Room AC Sizing Quick Reference
Room Size Typical Lights Baseline BTU/hr w/ 20% Headroom Recommended AC Size
4×4 ft (16 sq ft) 400–600W LED 1,364–2,046 1,637–2,455 Portable 8,000–10,000 BTU
4×8 ft (32 sq ft) 800–1,000W LED 2,728–3,410 3,274–4,092 Portable 12,000 BTU / 1-ton mini-split
10×10 ft (100 sq ft) 2,000–3,000W LED 6,820–10,230 8,184–12,276 1–1.5 ton mini-split
12×12 ft (144 sq ft) 3,000–4,000W LED 10,230–13,640 12,276–16,368 1.5–2 ton mini-split
20×20 ft (400 sq ft) 8,000–10,000W LED 27,280–34,100 32,736–40,920 3–4 ton mini-split or central

Frequently Asked Questions

How many BTUs do I need for my grow room?
The baseline rule is 3.41 BTU per watt of lighting per hour. A 600W LED generates about 2,046 BTU/hr from lights alone. Add heat from equipment, dehumidifiers (nearly 100% of their wattage), and ventilation infiltration to get the complete picture. Always add at least 20% headroom so your AC isn't running at maximum capacity all day.

What size mini-split do I need for a grow room?
Mini-splits are sold in tonnage: 1 ton = 12,000 BTU/hr. Divide your total BTU requirement (with headroom) by 12,000 to get tonnage. Standard sizes are 1, 1.5, 2, 2.5, and 3 tons — always round up to the next size. Mini-splits are the preferred choice for sealed grow rooms because they dehumidify as they cool, and their efficiency lowers operating costs compared to portable ACs.

Does a dehumidifier add heat to my grow room?
Yes — significantly. Every watt your dehumidifier consumes is converted nearly entirely to heat inside the room. A typical 300W dehumidifier adds roughly 1,023 BTU/hr to your cooling load. A 500W commercial unit adds over 1,700 BTU/hr. Always include dehumidifier wattage in your BTU calculation — it's one of the most commonly overlooked heat sources.

Can I use a portable AC instead of a mini-split in my grow room?
For small spaces (up to ~4×8 ft with ≤1,000W of lights), a portable AC can work. For anything larger, a ductless mini-split is strongly recommended. Portable ACs are less efficient, they need exhaust ducting (which can disrupt pressure and introduce pests), and their rated BTU is often overstated. If you're running a sealed room, a mini-split is the only viable option.

Why do I need a safety headroom percentage?
Running an AC at 100% capacity continuously shortens its lifespan and makes it unable to handle peak heat events like hot days, door openings, or adding more equipment. A 20% headroom is the industry standard. Use 30% for sealed rooms where heat builds quickly, or if you plan to add equipment later.

Ready to cool your grow room?

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