1000 watt lamp inc radiant heat 4,000 BTU
1000 watt magnetic ballast 3,500 BTU
1000 watt digital ballast 2,500 BTU
600 watt lamp inc radiant heat 2,400 BTU
600 watt magnetic ballast 2,100 BTU
600 watt digital ballast 1,500 BTU
This information right here is grossly inaccurate.
First off, lets talk for a short bit about the amount of energy that is emitted from a light bulb. A 1000W light bulb will emit 1000W of energy, for all intent and purposes. As most high power bulbs age(>10,000hrs of run time), they increase the power draw, usually peaking around 1100W. So, lets use this 1100W number for the bulb. Photosynthesis is a process that is approximately 1-2% efficient in most plants(sugar beets are an exception). HPS bulbs emit light at approximately 20-25% efficiency. So, the plants are absorbing 2% of 25%, or 0.5% of the energy emitted from the light bulb. 99.5% gets converted into heat. Basically, you need to account for 100% of the energy emitted by the bulb.
The unit conversion from W to BTU/H is 3.412. 1000W=3,412BTU/H.
1000W HPS lamp near end of life, 1100W = 3,753BTU/H.
Now lets talk about ballasts. A ballast is a transformer, essentially. They are typically 92-97% efficient. The worst of them at maybe 80% efficient. This means that a ballast that is 80% efficient that delivers 1000W of power, draws 200W more from an outlet and emits that 200W as heat, hence the cooling fins ballasts tend to have. Or 1200W in total. So, lets assume we are at end of life again, 1100W of HPS lamp means 220W of ballast power usage/heat.
220W = 751 BTU/H
For a 600W lamp, end of life, 660W end of life power draw = 2,252BTU/H
+ ballast @80% efficiency = 450BTU/H
1000W Bulb, Combined: 4,504BTU/H
600W Bulb, Combined: 2,702BTU/H
The last thing you need to consider is energy entering the room from equipment like pumps or fans. A pump in the grow room to circulate water in the hydroponic system? A fan to ventilate air? Account for 100% of the power rating of the motor that drives it.
A 1hp pump = 746W
A 1/8hp ventilation fan = 94W
You get the idea.
Lastly, you need to consider the temperature of the outside of the grow room. If you are growing in a tent, you shouldn't have much trouble as long as you are ventilating that room really well in addition. Basically, you want to keep the area outside the tent the same temperature as the inside. Maybe 75-80°F. If you can do that, you aren't adding heat to the tent. If you aren't in a tent, and are in a complete room, you need to pay attention to the temperature outside. Hottest days are 95-105°F? These need to be accounted for. Ventilation will not suffice as you are bringing in hotter air from outside during these summer months. A rule of thumb that I have used in the past as a mechanical engineer works like this:
A = Measure the Area of the walls on the exterior.
dT = Maximum temperature differential between outside and your grow room. Usually a 40°F differential is the largest you'll see. That's assuming 75°F grow room at 115°F Arizona summer heat.
R = insulation value of your wall. Don't know? Assume R3 insulation. R = 3. If it is just a singe piece of plywood wall, with no drywall(like an attic) assume R = 0.62. 1/2" plywood, R = 0.62.
A*dT/R = BTU/H heat gain due to environmental factors.
Example: Attic grow room. 1/2" plywood + shingles = approx R1.5. Total roof and upper wall area = 600 ft^2. 40°F dT
600*40/1.5 = 16,000 BTU/H
Add everything up. Add the total amount of lights. The total amount of motors. The heat gain from hot summer days.
Now, it is always good to have a larger cooling system than the load that it is design for. This is how every commercial HVAC system in the world is designed. Always implement equipment that is 15-20% greater in capacity than the design load.
Multiply the number you just got from adding everything up by 1.2. Go find the next largest piece of HVAC equipment you can find. It can be a window unit, a split system, etc.