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How many CFM to cool 400w HPS? Help

Discussion in 'Grow Room Design & Setup' started by CommieChase, Apr 10, 2009.


    CommieChase Well-Known Member

    I have a DR80 which is 2.8 x 2.8 x 5.3 & a 400W HPS to put in it. I am looking into inline fans and I was wondering what would be a good enough CFM to pull through a carbon filter & cool tube and make sure the tent doesn't get to hot. I was looking into a 170 CFM 4" inline fan. Think this would keep this tent cool enough, even through a carbon filter & cool tube?

    olosto New Member

    Im running a tent slightly larger and the 4 inch thru cool tube up thru attic and scrubber and it works good.

    TheOrangeJuicer Well-Known Member

    I use a 170 CFM 4" Inline fan to cool my 600W HPS through a cooltube. Works great, temps were around 80 to 85.

    MrJoshC Well-Known Member

    Hey thanks, I am putting together something very similar and wasn't sure if it would work. I guess it will :)

    krunchy Active Member

    I'm also using a 600w HPS with a cool tube, and a carbon filter attached as well. Its worked well for me with 5 plants.

    RandyRocket Well-Known Member


    hippiepudz024 Well-Known Member

    i use a 165 cfm squirrel cage fan for my 400 watt light so i can put my light about 8 inches away from the tops

    CommieChase Well-Known Member

    Alright, thanks guys. I guess I'll be getting the 170 CFM inline fan for my 400W HPS. It isn't going to be getting blown into another room though. Just in the same room that the tent is sitting, but the door will be open to the room. Think this will affect the temps much?

    BigBudBalls Well-Known Member

    Its an open ended question. Duct size? Bends turns? how many? static pressure of the fan? length of the run total? Pressure drop end2end? etc?

    But, forget all that (for the most part) You don't need much, but do need a quality fan. (forget the $30 inline booster fan from home depot) Anything above 150CFM should work. I'm using a S&P TD-150 running at the slower 213 CFM and *more* then enough. But I have that cheapo mentioned above and it is/was *useless*. The S&P only takes care of the light. No carbon filter, no room venting, just the light. Multitasking a fan is a kludge, as best.

    tejastoker Member

    how many cfms?

    CanadianEh Active Member

    I'd say open hood you can use PC fans to cool it, to be safe i'd recommend at the lowest one 240 CFM 6" duct booster fan (Home depot will have this).

    400 watts dont get too hot, you can always use open hood and you only need a pc fan for intake / exhaust.

    bazookajoe Well-Known Member

    I have a 295 cfm with carbon filter and cooltube and I can hold my hand on the glass all day... doesn't even get warm.. cpl 90's in my run but temps and RH are stable and airflow isn't an issue, light is prolly 6" from top of tallest mom. Had issues last week cuz I had the light to close(>3") .. they weren't burning but creasing upwards to protect themselves from the light getting "bleached".. anyways.. 295cfm is great uhh yea... stones n ramblin

    fir3dragon Well-Known Member

    400w does get hot if you live in a warm climate. i had a open hood 400w and was batteling 95 degree temps inside cab 80 outside.

    unity Well-Known Member

    Sorry guys, but that is a rather 'loose' way to approach this. There are a view more (ha, understatement) things to consider here :
    - heat load of the air used to cool light
    - fan performance table at a given static pressure, meaning how much resistance is the fan exposed to i.e. duct turbulence, carbon filter, overall duct length, duct turns and restrictions etc.
    For example if a fan gives you a cfm delivery rate of 170 cfm, that number is meaningless without the associated static pressure at which it can deliver this airflow. so, 170cfm at .1" of static (commonly used) means that the fan can move 170 cfm (cubic feet of air per minute) as long as the fan experiences vitally no resistance (.1"), which it does not since you have ducts, hood, scrubber etc. hooked to it. A far more realistic static number would be .5"-.8", which will cut your cfm rating close to half!!! So, keep this in mind when shopping for the next fan. PERFORMANCE TABLES MATER!!!

    unity Well-Known Member

    Without static pressure readings all your cfm numbers are meaningless,
    I call major bullshit on this thread!!!!

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