My electric bill is nominally higher,.. not really much, but i have a veg box, with a 150 watt HPS cool tube,and 150 watts of cfl light also... He's right, a 400 would be better, but i got a smokin deal on 2-250 watters I just couldn't pass up... I built my flowering cab out of an old metal 2-door locker... you know the kind, with the bar for hanging stuff in it? So I have a basically 24x 18 x 40, with a section walled off with shelves for my ballast, fan, and nutes, etc. I modded the hood a little bit, cut a hole and added some ducting, it kinda works like a restaurant hood, no lens on it..but i may still do that. So a 250 works for me, and I have another 250, I'm not using right now,... when I get a new cam, Ill post my pics,... I'm far from a carpenter, but hey, shit grows in 'em and they work well for me!
the kinda guidelines I always got were... 150 watt hps... 14" square
250 watt hps...18" square
400 watt hps....24"square