Continuing the discussion from Grow room self made:
I’m not sure distance of plants from source of air intake makes a whole lot of difference. The intake air will get mixed with the air inside the grow space. Usually you want the intake air to be cooler than the grow space air. That is why, for example, the intake is at the bottom sidewall of a tent. And, the exhaust air outlet is at the top of the space. The negative pressure caused by the exhaust sucking air out causes air movement and exchange of “fresh” air for stale air.
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Thanks beardless. Time to go clean my grow spaces and work area and get ready for the next grow season to start.
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No problem. I just cleaned up from last grow too. Always a new beginning.
I have an 18inch box fan to draw in fresh air would two 4inch exhaust fans be enough to draw out the heat on 600w HPS.
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I know I’m stepping in late, but it sounds like that set up will give you positive pressure - not what you need.
Is your HPS sealed - like a Cool Tube? 
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I have no idea how much heat an HPS produces. i have LEDs. Also the temp of air source has a major impact on it ability to moderate the heat produced by the HPS. The primary question is what is the exchange capacity of your 4" fan. i.e. CFM cubic feet per minute. I believe the rule of thumb for grow room air exchange is 100% every 3 minutes. So, if your fan is rated at 150cfm it supposedly can handle 450 cubic feet at 100% efficiency. You will have to do the math to meet your conditions.
I grow in a 3x3x7 tent. That is a whopping 63cf. I have a 6" exhaust fan rated up to 330 cfm. I also run a 6" terra bloom intake fan rated up to 350 cfm. At max speeds I can basically suck my plants out of the tent. Kidding - they are just more than I need. I run the intake at slightly lower speed than the exhaust so to create minor negative pressure.
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My recollection is that 1 watt of HPS creates just as many BTUs as 1 watt of LED. 1 watt hour puts 3.4 BTUs out somewhere. Hard to put that into relative terms, but an HPS bulb that’s been on for a few minutes would absolutely burn you if you touched it.
If your exhaust and intake are sized properly you should be able to run that system with passive intake. Ie, no intake fan needed.
What is flange size on your hood? I feel like most of them are 6", therefore running a 6" usually makes the most sense. From there you need to make sure you’re getting proper air exchange for volume of your grow space, like the others said.
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Those lights will get hot. If you have a big enough area it’s no big deal with multiple lights. If you have a hood that needs to be air cooled do you need to air cool it. Because it will make your light run to hot which then messes with the gas is on the inside not only that your wires that your lights run off will get hotter. Hotter wires less efficient. I run high pressure sodium I have 1000 w and 600 W. If you touch that hood it is hot if something lands on there and gets dry enough on the hood also dust. Also the distance of your light from the ceiling. You will burn not only will you burn your plants you will burn your house down.
yes I’m gonna run 3inch computer fan on my light to help cool it down. Burnt myself a few times
I can tell you what you can do in the center area underneath your plants where your lights at you need a fan blowing on that upwards. A good fan not necessarily expensive fan that will help with your heat you have to keep that Light cool
Send me a picture of what you got if you don’t mind let me see your light let me see what you got going on maybe I can help you but you do need a fan you have got to keep that stuff cool you will not be able to lower your lights your buds will veg the whole time. Not saying you’re grown won’t be any good it just wouldn’t be a strong. 600w hps I wouldn’t even run a white light. They tend to get a little hot.
I have ran 400w with no problem. Not in a tent. Or exhaust fan.
I don’t do Amazon you can get that fan right there for $40. This is my back up Fan. Never been used. I run 8 in to a four. I have 100% control of my heat air everything. Because I am lucky right now. I got to go to a tent which I have and 100% LED lights or I’m I have to build a room which I think I’d rather build a room. Just be careful man
ill try to get better pic later on in the day all my ducting is 4inch so I want to dbl up the exhaust
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You’re veg right now correct
These lights are cheap they are OK maybe to veg. Home Depo i’m sure other places have them also. I don’t use us to grow well I just happen to get a light for my sink.
I’m sure you could get a used hood with a cover if you check around some grow stores. The fans are use are not very good so I will have to upgrade at some point. @Breezy Has a nice set up
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Thanks for the tag! I’m running a GGT 2x2.5x6’11. HLG 135 v2 rspec and AC Infinity T4 for exhaust. No intake fans. Someone above already covered it, but I just leave the velcro flaps at bottom open for passive intake!
Good Luck gromie!!
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What are you using digital? Hps? In my opinion I don’t really know how big your tent is but I don’t think you need all those lights. I can understand if you’re trying to veg. But you can do that with a hps. I use hlgs 4000k as supplemental light. You have to be careful with that also because as your light goes out heat. It will put too much heat on the LED. If your in a 4x4 get leds if you can. 400w with a 4K light will grow. Your tent will be like 200’ f. I can cook food on that