Free calculator

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

Grow lights (total draw)WOther equipmentWFans, pumps, controllers, CO₂ gear — everything else that draws power in the room.DehumidifierWCompressor dehumidifiers add their full draw as heat while running.

Result

Includes a 1.2× safety factor

Cooling capacity needed

3,071BTU/hr

= 0.26 tons = 0.9 kW of cooling

Raw heat load

750W

Nearest standard unit: 5,000 BTU/hr. Mildly oversized is fine — grossly oversized short-cycles and dehumidifies poorly.

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 →