AC / BTU sizing calculator
In a sealed grow room, every electrical watt becomes heat the AC must pump back out: lights, fans, pumps, and especially the dehumidifier, which returns all its power to the room as warmth.
Heat sources
Result
Includes a 1.2× safety factor
This covers equipment heat only. Sun-exposed rooms, hot climates, poor insulation, or heat-throwing gear in adjacent spaces add load a full Manual-J calculation would catch. If the room is vented rather than sealed, the exhaust fan removes much of the light heat first.
Venting instead of sealing? Size the exhaust fan → Curious what the AC adds to the bill? Electricity cost →
How many BTUs do I need to cool a grow room?
Add up the wattage of your lights and equipment, convert to BTU/hr at roughly watts × 3.41, then size an AC unit with headroom for ambient heat gain and duct losses. Undersizing is the most common mistake, since grow lights run a near-constant heat load unlike a bedroom AC that cycles off. Enter your equipment wattage above for exact BTU/hr and tonnage.