3.5' x 2.5' x 7'.... 400w vs. 600w?

OK, i realize the 400 vs 600 question has been asked more than "how much will i yield."

I've spent a lot of time searching but haven't found a solid answer.

My cab will have inside dimensions of 42" wide X 30" deep X 84" tall. Works out to 8.75 ft^2 floor space, and 61.25 ft^3 total volume.

I plan on using a 6" inline fan for exhaust. Exhaust will go fan>light>carbon filter. I do not currently plan on having a dedicated air intake for cooling the bulb.

Should the exhaust setup work with a 600w and still keep ambient temp in check? Intake temp should be around 75*.

Obviously i would like to go for the 600w, but if temperature control is going to be too difficult i will just go with a 400w. If you think temps will be an issue with the 600 and the setup i have described what would you recommend to lower the temps?

many thanks in advance!

you want the light>fan>filter not fan>light>fliter. If you ambient temp around the room is 75, then I think you would be fine with a 600w. I just did a 400w grow and wish the bulb had been bigger. I have ambient temps of 85-100 and a 400w worked fine for me.

There is not so much diffence in heat generated between the 400 and the 600 however in a small space like the one you are describing cooling will be an issue. The 6" ducting will definatly help and because you are using such a large fan I would say to go with the 600w. It produces roughly 40000 lm more than the 400 so the extra light is worth it. Just make sure that you are blowing the heat out of the room not just into it. Air transfer is the most important thing, How much air flows into the room and out. You want an area of high presure on the intake compared to the outflow. Like I said air in and air out is the key to a cool grow room no matter what generates the heat.

I have a 600 watt metal halide and my space is a little bigger than urs with ambient temps of 70, it does get pretty hot and i've been debating the pros and cons of 400 or 600 still. At 3 feet from the light the temp sensor reads 87-90* but I don't have a fan sucking air directly off the bulb. One thing that might set ur mind at ease is would u rather get the 400 watt and after he grow think "That was nice I didn't have any problems with heat, but what could i have done with a 600 watt?" Whereas if u get the 600 watt u can finish the grow thinking of how much you yielded, and know u struggled with the heat and pushed ur growing abilities to the max with what space you had. Also you CAN put a 600 watt bub in a 400 watt ballast, it might put out slightly fewer lumens but the starting voltage and required current to run are about the same from 250-1000 watts. So u can buy a 400 watt ballast and get a 600 watt bulb and just return bulb to the shop and get a 400 if its too much heat.

Sound like you're all confirming what i was pretty set on....looks the 600 gets the nod!

when you get that light let me know how it fits with ur grow room, I've got a grow room about the same dimensions but mine isn't properly ventilated, it would help to get an idea of what proper ventilation could do.

Well, a little over 3 months has passed and the cab is built, painted and almost ready to go!

Final dimensions ended up being 4ft wide, 3ft deep and 6 1/2ft tall.

My digital ballast 600 and air cooled hood should arrive this week, along with my Tjernlund 6" inline fan (530 cfm)

Will update with ambient temps once everything is together and running.