Quote Originally Posted by cornish_dope
If you can't afford the ventalation aswell as the 1k don't bother because your plants won't live long.
I definitely agree with that.

The 1k system is going to heat up just about any room, and would almost certainly be more useful air-cooled. A non digital 1k ballast will also add some extra heat to the room it's in. If you can get the fans, ducting, a/c hood, etc., I'd use the 1000w all day long. But if you're just getting started with HIDs, and can't afford to put much into ventilation at the moment, the 400w would probably be more feasible.