400-600 heat difference

I am in the market for a hps/mh setup. Is there a big difference in the heat from a 400watt bulb to a 600watt bulb?

Somewhere I read that it's the metal halide bulbs that really put off the heat so could someone verify that please? What's the difference in heat if someone knows statistics. The room is a normal bathroom size with a nice window for true ventaliation. Being the current cfl grow won't be done until August/September the heat will be less of a problem because the cooler temps will be here for the winter 1st time hps/mh grow. Waiting is like being at the top of the stairs on xmas eve as a kid. Cross my fingers and knock on wood but I've had great luck with my 2 grows so if I can get over 2 z's off 1 plant with cfl's and care/love/attention to detail then I should be really able to yank some greenage with a 400-600 watt combo light.

I'd say the difference is significant, but not massive. I live in SoCal and I use a 600W light in a grow tent. Temperatures here fluctuate quite a bit day to to day so I really have to be on top of things. I'm reasonably certain that a 400W light would require less effort on my part. If temps aren't too bad where you're at, I don't see why you couldn't go with a 600. Also, I can't say I've noticed a difference in heat between MH and HPS bulbs.

mh bulbs do give out more heat but the temp dif between the 600 and 400 isnt really that much dif (5 degrees maybe) if ou have proper ventilation tho its no prob at all if your going for a lot of plants tho you will prob need the 600.