If you use 220V for your grow room it cuts your AMP load by half...and personally i prefer running on 220 i feel much safer. So if its a option you might want to consider doing that.This might come in handy and dont load a circuit to more than 70% of its load , you can go 80% but i always try to be safe.And another thing i'd do is make sure of my breaker APM rating. Each area has different electrical codes, so what might work for someone else might not work for you. Happy grow

watts/volts = amps

600w/120v = 5.0 amps
600w/240v = 2.5 amps

1000w/120v = 8.33 amps
1000w/240v = 4.16 amps