Calculating Heat Load Heat is measured in either BTU or Kilowatts. 1KW is equivalent to 3500BTUs. The heat load depends on a number of factor's 1.The floor area of the room 2.The heat generated by equipment 3 the heat from lighting 4.The number of room occupants 5.The ambient temp ( your room's starting temp ) this will be added asap im still playing with the #'s 1.Floor Area of Room Room Area BTU = L x W x 40 ( H = 8foot + 5btu per foot after that) If you have a wall that is facing the sun add in for the extra heat Sun facing wall BTU = L x H x 40 2.Equipment This is trickier to calculate than you might think. The wattage on equipment is the maximum power consumption rating, the actual power consumed may be less. However it is safer to overestimate the wattage than underestimate it. Equipment BTU = Total wattage for equipment x 3.5 Ballast in room BTU = ballast wattage/2 x 3.5 3.Lighting Lighting BTU = Total wattage for all lighting x 4 Air cooled hood BTU = wattage x 4 / 2 @ 400= 200-250 cfm 600= 250-300 cfm 1k = 300-350 cfm ^ is just a guide cfm per hood will be on your ducting/SP.... 4.Occupants even being that im only there for 2 or so of the 12 hrs i like it to be able to handle the extra sweat when i smoke one. Total Occupant BTU = Number of occupants x 400 Total Cooling Required Add all the BTUs together. Total Heat Load = Room Area BTU + Total Occupant BTU + Equipment BTU + Lighting BTU I can't remember what book I got this info from or I would credit it. ~HD