Strangely enough, my gf thought something similar when we were at my old apartment, although she wasn't sold that it was my grow because we had suspected our former roommate was being a turd, and sure enough, towards the end of our time at that apartment, it was nice out, maybe mid-70's, and his door was closed.. I knocked, thinking he was home, and when I heard something in the room, I opened the door, and he had the AC on full-speed.. Turns out, he left the day before, and didn't come back for 2 days, so every time he had left, he did the same thing; left all of his appliances on in his room.. Turns out my grow only costs me roughly $13-18, depending of if I'm germing seeds or just growing and I have a Mars II 400w (192w true), a quad of 23w CFLs, a couple small 6" fans, 1 6" inline fan and the air pump, so I'm looking at roughly 400w of power being used, on a 19/5 schedule..
Women.... lol