Equipment
Lights, fans, meters, sensors, calibration, controllers.
Calculate it properly: AC and cooling load for a grow tent or room
Your cooling load is every watt you plug in, times 3.412 BTU/h, plus heat through walls and from people. Lights, drivers, fans, pumps and the dehumidifier all count. Plants don't add heat; they turn some of it into humidity, and a dehumidifier turns it back into heat. A sealed 10×10 ft room with about 3,300 W of LED needs roughly 16,000 BTU/h (1.3 tons) of cooling with dehumidification, before a 10–20% margin. Prefer a mini-split to a single-hose portable unit.
Calculate it properly: dehumidifier size for a grow tent or room
Plants transpire nearly all the water you give them, so a dehumidifier must remove roughly what you water each day, minus runoff. Measure it in litres or US gallons, convert to pints (1 L = 2.11 pints), and add 25% for lights-off peaks. A 4×4 ft tent in flower using 4.5–9 L a day needs about 12–24 pints a day of rated capacity. Since 2019, US labels are tested at 65 °F instead of 80 °F, so the same machine now shows a smaller number.
Calculate it properly: exhaust fan CFM, intake size and carbon filters
Size an exhaust fan for the bigger of two numbers: one air change a minute (CFM = tent volume in ft³) or the heat it must carry out (CFM = BTU/h ÷ (1.08 × temperature rise in °F)). For a 4×4×6.5 ft tent that's 104 CFM for air changes but about 190 CFM to carry 600 W of heat out at a 10 °F rise. Then allow for the carbon filter, ducting and bends using the fan's curve. Use passive intakes about 2–3 times the exhaust duct area for slight negative pressure.
Calculate it properly: how much grow light your tent or room needs
Size grow lights from the light the plants need, not from watts. Pick a PPFD target (about 900 µmol/m²/s for flower at ambient CO₂), multiply by canopy area, divide by about 0.85 for photons that miss the canopy, then divide by the fixture's µmol/J. A 4×4 ft tent needs about 525 W of a 3.0 µmol/J LED, 605 W at 2.6, 685 W at 2.3 or about 925 W of double-ended HPS. Then hang it to get even light, checked with a PAR meter.
Calculate it properly: watts, amps, circuits and 240 V for a grow
Amps = watts ÷ volts (÷ power factor for AC gear). Grow equipment runs for hours, so codes treat it as a continuous load: keep it to 80% of the breaker, about 1,440 W on a 15 A 120 V circuit, 1,920 W on 20 A 120 V, and 3,840 W on 20 A 240 V. A 4×4 ft tent with lights, fans and a dehumidifier fits one 15 A circuit; a 10×10 ft room needs several 120 V circuits or a 240 V circuit plus a dedicated one for the AC. Use GFCI protection, no daisy-chained power strips, and a licensed electrician for new circuits.
Grow-room calculations: size lights, cooling, dehumidifier, CO₂, fans and power properly
Size a grow in this order: light first (PPFD target × area ÷ efficacy), then the heat it makes (every watt is 3.412 BTU/h), the water the plants transpire (about what you water), the airflow or AC to remove both, CO₂ only if the room is sealed and bright, and finally the circuits to power it all at 80% of the breaker. Each step has a guide with formulas in metric and imperial and worked examples for 2×4, 4×4, 5×5 and 4×8 ft tents and a 10×10 ft room.
LED drivers explained: 120 V vs 240 V, real watts, and Mean Well vs Inventronics vs Sosen
The LED driver decides how many watts reach the diodes. Most drivers are slightly less efficient at 120 V than 240 V (Mean Well HLG-600H about 94.7% vs 96.5%), derate at low input voltage and high temperature, and only give full power inside a set voltage or current window. In the founder's experience, many budget panels deliver about 80% of their advertised watts. Datasheets from Mean Well, Inventronics and Sosen show real trade-offs in efficiency, surge protection, life rating and warranty; no-name drivers can't be checked.
LED vs HPS: the heat and power-bill myth
Contrary to popular belief, watt for watt, an LED and an HPS heat your room exactly the same: every watt is 3.412 BTU/h of heat, whatever the device. LEDs only save power and heat when they make more light per watt. Independent tests show double-ended HPS at about 1.7 µmol/J and the best LED fixtures at 3 µmol/J or more, so a top-tier LED needs about 40% less power for the same light. That edge belongs to the top tier only, and the house advice is still to swap watt for watt for more light.
Samsung LM301B vs LM301H, bins and fake chips: an LED buyer-beware guide
Samsung's LM301B and LM301H were the same chip with different datasheets: a Samsung rep told GenetixBay so in 2019, and our lab test of LM301H vs LM301B builds measured the same while the H parts cost about 20% more. What matters is the brightness bin, drive current, heat, the driver and authenticity. A genuine low-bin chip pushed hard on a budget driver gives about 2.3 µmol/J at the fixture; a top-bin chip run gently about 3.1. Samsung ended all LM301 production in 2025, so check reel codes, lab tests and DLC listings.
