2x4 room 400w hps ventilation question

My flowering side is almost setup.. All I have left to do is ventilation for the room. I can easily vent outside(to the right of the hps in the pics) and have an intake on the left side from the room next to my basement which is usually cool. The area that I am working with is about 2x4x6.5ft. According to an online calc the most I would need to exchange air once every minute is about 65 CFM. Both my intake and exhaust need to be in the rafters.

I was planning on using a 4" inline ducting fan to exhaust out.
http://www.lowes.com/pd_234523-1061-DB204_0__?storeId=10151&Ntt=4+inch+duct+fan&UserSearch=4+inch+duct+fan&productId=3089849&N=0&catalogId=10051&langId=-1 (rated @ 65 CFM)

I know that I need to have the intake fan have a lower CFM then the exhaust to create negative pressure. I was planning on using a 4 inch pc fan for the intake that is about 35 CFM.

Here is where I am kinda lost on the most efficient way to do this. Should I run ducting from the intake and through my hood to the exhaust? If I were to do that where would I put my carbon filter? Or could i also put that on a seperate exhaust? Also I'm guessing I would need to get a piece of glass cut for the hood as well.

I was also thinking of just having the intake blow into the room with no ducting and then doing something like fan > carbon filter > hood > ducting to exhaust. I really don't have a clue what I am doing here :\ any help or different ideas would be much appreciated!

In order to effectively cool a 400w HPS you are gonna need a 5inch with around 200CFM's of power.


If your hood is air cooled you can go.


FILTER --- HOOD ------ FAN ------- EXHAUST.


You could then use just passive intake holes.



J

Thanks for the reply! From what I've seen from other posts I'll make a 2-3 4inch holes for the passive intake on the opposite side. Should I duct the intake down closer to the bottom of the room or will it be fine in the rafters? I assume these intakes should be screened. I was going to add an "S" (2 90 degree elbows) for the active intake i had in mind to prevent light leaks. Is this the best option or is there an easier way for a passive intake?

couple tips for a new op that are handy.
Let your temp decide what size intake and exhaust you need, especially with a 400w. You might not need to exhaust at all during veg, and if so then you only need to run your fan and filter during flower, and at that point you'll probably only exhaust to scrub the air.
Use the size of the room to pick the carbon filter you want, and then use the fan the filter is rated for.
65 cfm might swap the air out in the room, but the smaller carbon filters still require 140cfm and up to adequately pull air through the filter.

So turn on your light for an hour and put a thermometer a foot above your plant sites. If your temps are below or at 85 you'll be fine, if they're close you can get away with taking a $10 oscillating fan and screwing the base into the wall of your op. Viola! instant house fan for plants, and it'l drop your overall temp on the plants a few degree's - as well as give you better stem developement and air flow to prevent bud rot.
If your temps are over 85 after an hour you need exhaust, so then you can just mount some clamps or a bracket on the raftors to hold the filter inside the op, and cut a hole in the wall and mount your fan on the outside, and screw the two together. a 6 inch fan pulling air out of your op is going to need a 4 inch intake hole, you don't need a fan to pull air in, the displacement will do it for you. Intake fans are more handy for pulling air from one side of a building to the other then just feeding it into a cab, and in the end you're saving money.

Edit for additions -
Inline fans aren't exhaust fans, they're inline fans for correcting the loss of air movement from pulling air over long distance, or through 90 degree turns. The blades are smaller so they provide less air resistance in the duct, but they pretty much just keep air moving when an exhaust fan is too far away from the air source.
I couldn't get the link to lowes to work for some reason, so I dunno if thats what type of fan you have in mind, but a bathroom exhaust fan is around 70 to 90 CFM for a point of reference.

edit again already - got the link to work, thats an inline fan not and exhaust fan

intakes should be positioned near to the floor.

ALL INTAKES SHOULD BE SCREENED .

Elbows are ok as light traps but can restrict airflow. I tend to duct mine where they're needed and paint the inside black.




J

Left it on for an hour and it was around 88-93F about 18 inches from the lamp. So when you say an inline fan is not the answer are you also speaking of can-fan/vortex inline fans or just inline duct fans? So fire, I am a bit confused on your positioning for the exhaust setup. Are you saying I should go Carbon Filter > Air Cooled Hood> Ducting to wall > Exhaust to outside vent? Right now I'm looking at something like this squirrel cage. Dayton 273 cfm Exhaust Fan w/cord Would this carbon filter be suitable? 200cfm 6" carbon filter

Would I be alright to just duct the intake from the ceiling/rafters to somewhere lower then since i have no other viable place to put an intake? Would that also mean that it would require an active air intake because of the 4-5 foot of ducting?

I apologize for being such a noob. It's not that I haven't researched this(although I obviously haven't enough)... I just can't seem to get this right >.>

inline fan is totally different than a can/vortex fan. They are much stronger. Inline fans are just meant to keep air moving, not pull air through a filter etc etc. They are just not strong enough. If anything go too big on your fan needs and then slow them down with a controller if need be. It is one of those purchases that seems like way too much money but it is essential.

Understood. I could tell that theres a major difference in power etc they're just listed as "inline" fans also.

That fan and filter you listed would work just fine but I would just get the combo from HID hut for $200. I know that can fan is solid. Not sure about the other one.

You have the airflow right in your description above. I think you passive air intake should work fine even with the small duct run. Could always throw the cheap inline booster fan in their if need be.

Also make sure your air cooled light hood is sealed if you go

carbon----light-----fan----exit. If you have air leak in your hood you are going to get odor out. Just thought I would point that out as some hoods let air in.

Nice setup you got there.

I looked at your pics again. Do you have glass and exit/entry ports on that hood to cool it directly? If not then you can't really run your scrubbed air through the hood and might just be best off running your vent without air cooling the lights. Just hang the fan/filter at the top and then vent out with the cooler air coming in from below. I run a 400 in about that same amount of space with no heat issues but my intake air is usually in the 50's or low 60's.

It would be easy if you could put the carbon in the middle but they do not work like that.

Yes there are 4 inch exit/entry panels that are removable on the sides of the hood and I will most def get glass cut when everything is up and running.

The White Buffalo said:

I looked at your pics again. Do you have glass and exit/entry ports on that hood to cool it directly? If not then you can't really run your scrubbed air through the hood and might just be best off running your vent without air cooling the lights. Just hang the fan/filter at the top and then vent out with the cooler air coming in from below. I run a 400 in about that same amount of space with no heat issues but my intake air is usually in the 50's or low 60's.

It would be easy if you could put the carbon in the middle but they do not work like that.

Click to expand...

I ended up getting a combo similar to what you mentioned. 6 inch can fan with a carbon filter. I'd rather go too big then too small as I may expand the room 2 feet wider at a later date.

This is in a basement and my air in the next room generally says 72-75ish year round. so everything should be stable once its up and running. Thanks for all the helpful replies everyone!