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Push or Pull? Fan Air Movement through Hoods?

Discussion in 'Grow Room Design & Setup' started by ectoendomezo, Jul 25, 2011.


    ectoendomezo Member


    Suck Or Blow..Nyuk!

    1) In the old day's..I was told.."Push The Air Through The Hoods".(Blow)

    That is to say..the Fans are set to "Push Air Through And Out" and thus a series of filters becomes necessary etc..etc...sigh...etc..

    I now believe...this is questionable/debatable.

    I believe the Old Wisdom for this..was "Scent and Security Issues"..as opposed to straight-up "Efficiency".

    2) Out of basic necessity of "Events"..I've recently set up a "Suck" System with Hoods (Reflectors) simply "Sealed" at one end. (Scent/Security is not an issue 'round here.)

    Hood Surface Temperatures are.....vague..thus proving little. That is to say..temperatures taken and 'felt' on the Hood's..for both the "Blow Line" and the "Suck Line" seem..basically..Equivalent. Measuring "Fan Stress" and the rest of the Field of potential measurements well..perhaps I can obtain answers here instead of bringing in MIT?

    Before I do..ALL Hoods this way (And I am debating this 'internally' for the simple reason that I could literally Eliminate an entire "Network" of Ducting and Filters with a "Full Scale Suck/Pull System") I am wondering if any of you "Big Brains" out there..have any Real "Physics" or other "Certainties" which I might utilize to make the correct decision regarding this issue.

    Here are the Issues I hope to address..or that are important to..well..me personally in this decision:

    1) Heat (Always, and I'll literally take a "Degree or two" as "Enough Of A Reason")

    2) Equipment Fatigue.

    3) General Efficiency.

    Any SOLID information/Ideas are greatly appreciated.
    Little Tommy

    Little Tommy Well-Known Member

    I always pull through the light. Seems to give me better throughput this way. It also leaves my tempered glass less dusty.

    iNFID3L Well-Known Member

    why not just try both ways, and find out, i say this because either way wont hurt your plants, its a case of ''suck it and see'' as we say here in good ole blighty
    kbo ca

    kbo ca Active Member

    I like to pull air through my components after the air has been pulled through a filter just for cleanliness purposes. Nobody likes cleaning up a bunch of dust out of their fan and light hood after each grow.

    420God Well-Known Member

    It's more efficient to use the fan as a vacuum, you can move more air with less resistance.
    cary schellie

    cary schellie Active Member

    i just picked up an active air 400cfm for my cool tube, using it to pull air, i can place my hand on the tube now, allowing me to put my plants within inches, no turning back for me, cheap efficient set-up that takes my grow room down up to 15 degrees

    Muffy Active Member

    I have noticed that with square reflectors the heat can build up in the corners if you pull through. The air flow that way is a straight shot. If you push through the hood then the back pressure moves heat away from the corners until it finds the exit. In my experience this leads to a cooler environment for the plants.

    Scent shouldn't matter either way because the loop should be sealed. If you have a hole in the duct you could suck the stink into the duct or you could push stink out of the room because of positive pressure.

    Thundercat Well-Known Member

    I've been wondering the same thing, as I''m about to hook up a new 600cfm fan on my vent system. I currently just have 2- 6 inch duct booster fans that keep my 1000w antiquity cool, but I need more low to add a carbon filter. I've been trying to figure out the best configuration to possibly combine both sets of fans along the venting. I've been thinking about leaving the duct fans near the exhaust exit, where they are currently pulling air through the light. Then adding the inline fan right at my carbon filter pushing air through the system.

    iNFID3L Well-Known Member

    im just gonne use a 180sqm3 fan on intake and a 450sm3 on my lamp, one sucking air in, the other sucking out, job done.

    Kdn Member

    The fans we use will work more effeciently in a pull configuration with an open dump. If you duct the exhaust you then put back pressure and lower the fans effeciency so in the end it really doesnt matter(if your hoods dont seal all that well then pulling will help with heat leaks).

    Muffy Active Member

    Duct tap is cheap. :razz:
    Biologically Incorrect

    Biologically Incorrect Active Member

    I use an open end suck the hot air out through the lights system. This seems to work very well. Not having a filter also allows more airflow & efficiency like you are looking for. I also have an air vent right below the main light that is open, so I think this also helps suck some cold air through the lights, which makes them run a lot cooler. I'll post a pick so you can see what I'm talking about, but its pretty basic.

    Peace out
    Toolage 87

    Toolage 87 Well-Known Member

    I would say pull the air through or if you have 2 exact fans have 1 push and 1 pull.

    lol. no packing tape is cheap. You can get 3 ot 4 rolls where I live for around $1

    Muffy Active Member

    Apparently I was posting about tap. How many tap do you get for around $1?
    Biologically Incorrect

    Biologically Incorrect Active Member

    ???? I most be really HIGH! ???

    Muffy likes this.

    unity Well-Known Member

    Pulling will move more air & is therefore more efficient. 'Pushing through' the lights will cause a condition called 'turbulent' airflow, which will increase static resistance, and therefore reduce fan efficiency.
    Obviously, when we use co2 or when we are in a sealed environment we need to take great care in isolating the hood & connected ducting from the rest of the growing environment. This means, take super extra care while taping up the hood to ducts, the hood glass to the hood etc. I tiny negative leak will cause your co2 bill to go up in a big way ;)

    Cheers Kind

    unity Well-Known Member

    We don't have to try, the science is settled on this.

    unity Well-Known Member

    Cheers Muffy, the 'back-pressure or static pressure' you are talking about is actually a limiting factor as it relates to total cfm moved. Heat always moves from hot to cold, meaning that hot air in the hood corners will not be isolated like you might think. The more cooler air we get accross the bulb the more btu's we will remove, it is as simple as that.


    iNFID3L Well-Known Member

    well if thats the case with the air build up on pulling, just get a perspex replacement shield with a hole in each corner ?

    i hear what yah saying, but i cant work it that way, im flowering with a 400 and a large fan, temps are about 75-77

    Muffy Active Member

    Doesn't the back pressure change with the output of the fan? If we are limited to 10,000cfm but we only need 400 then it's nothing to worry about.

    Heat will naturally move toward cold but that is passive cooling. On a hot day you would be more comfortable in front of a fan than behind it.

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