Is that a sealed hood? With that setup you should not have to worry too much about heat, even with the 400w hps. However, you say that you are pushing air through the light and pushing air out of the box. You should actually be pulling air out. I made the same mistake, trying to make the fan push air through a bend and through my cool tube. My temps dropped a couple degrees by putting the fan at the end of my ventilation setup, pulling air through my carbon filter first, then the cooltube, out of the closet, and finally through the fan. I added some ducting on the end to help with the noise.

I keep my hps on the whole time during veg (after about the first week or two from sprouted seed), but if the cfls have the same output in Lumens, not watts, then keep the cfls. hps puts out about 50,000 Lumens per square foot. You could probably use both if you rearrange your ventilation.

Thinking about that basement, the temps should not go below 21 C, otherwise growth will slow. Is there any way you vent warmer air into the box from another room? Maybe try raising the box higher off the floor?

Good luck:jointsmile: