Go find the circuit breaker in your box that runs the plug you want to use,when you figure out which one it is it will say how many amps it is on it,also determine all the other plugs that run off it.Most household 120v circuits are 15 amps (so thats 12 amps usable if you go by the 80/20 rule),a 1000 watt ballast is usually around 9 amps running on 120v so you could only run 1 on that circuit but you could run another light off a different circuit.If you have alot of other shit plugged into the same circuits that could be an issue,you dont want to exceed 12 amps off any one 15 amp circuit at a time.
240v is just two legs of 120 put together,the same ballast that takes 9 amps to run on 120v only takes 4.5amps on a 240v circuit so you can run more on that circuit.If you were able to run a 15 amp 240v circuit that would be perfect for 2 1000's.The only real way to know if you have room in your panel to do this is to figure out how many amps your panel has incoming(usually 100 or 200,hopefully 200)then figure out how many your using and if you have room for any more.Take a picture of your outside panel and post it up and we can see what you have going on,each breaker might even have what it runs written down in the box if your lucky.
Also visit this thread to learn more and to get help from actual electricians,lol.
https://www.thcfarmer.com/community/threads/grow-room-electrical.46572/
