Alright, so i just came up on a 1000W HPS. I also have a 400W HPS. Right now i am rooting some clones. But when it comes time to 12/12 i only have about a 5x5x5 foot room in the attic, and it gets pretty warm on hot days. I would have a bunch of fans, but am worried about the top leaves because there is no air flow containing the bulbs heat. What is a good length to keep the 1000W at away from the plants? Do you think i should use the 1000W or the 400W?
1000 watt lamps need to be at least 18" and as much as 48" away from your plant canopy. In your 5' high space, you might be better off with the 400 watt fixture, at least until you can sort out a good ventilation system. You can keep the light closer if you have a light mover, but those take up more vertical space than mounting it directly to the ceiling.
your best bet in a 5 x 5 area is the 1000 watt that's what it is designed for 5'x5' so perfect. get a 6" can fan and exhaust the hood somewhere ele if u can get a speed controler for the fan to so u can set it so that the room stays the perfect temp while they r on. with the fan hooked up u can keep ur tops about 16"-24" away about 24" first 1-4 weeks of flowering then let the buds grow up to the light for the last last 4 weeks cuz they want that intense light the last month trust me love it.
You should test-drive the setup with lights to see how well you can manage temps (keeping in mind that they will be getting a lot warmer in the next couple of months). Attic grows are notoriously difficult because of temp issues, unless you are willing to invest in completely insulating that area and potentially installing heat and a/c. I tried an attic grow once and gave up, even on slightly warm sunny days the attic ambient temp would be 10-15F higher than outside, and in the growbox with lights on it was another 10-15F above that.
Thank you all for your suggestions. i think i am going to go with the 400 watt light because it will be a little less warm and i am worried about those sunny days when the temp. increases dramatically. I will need to get some good air circulation and will eventually put some pics up when i am done! suggestions always welcome!
Just remember that air circulation will only keeps temps down if you are exhausting the warm air and replacing it with cool fresh air. Moving warm air around doesn't make it cooler (even though a fan can make the air feel cooler to our skin, it really isn't any cooler).