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Thread: Reducing exhaust air volume (filter too small?)

  1. #1

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    Default Reducing exhaust air volume (filter too small?)

    My friend is growing in his attic space, his grow is stealthy so he connected a filter to his exhaust vent.
    The problem is that he connected the exhaust vent to the blower on the roof of his apartment building.

    The blower is way too powerful, when you stand in his tent you can feel actual breeze from the airflow as the blower sucks all the air from the tent,
    enough to make the plants sway without a oscillating fan.

    He is about to enter the flower phase and he is afraid his filter will not be sufficient.
    The exhaust duct is 5", and his filter is rated for 16,000 CFM
    (it was the largest one available for this diameter).


    1. Can someone recommend a way to reduce the airflow so no odor will leak out?
    (For example, will clogging half the duct with tape change the volume of air, or will just increase the pressure?)

    2. Will adding smaller filters that will filter circulating air in the attic to reduce the load from the big filter help at all?
    (He has 2 duct fans rated to 5000 cfm with matching 5000cfm filters, he thought to just let them run inside the tent)

    3. How can we measure the current airflow to know what is the blower rating
    (we have no physical to the blower, it's in the machine room on the roof).

    Many thanks!

  2. #2

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    Quote Originally Posted by BananaLizard View Post
    My friend is growing in his attic space, his grow is stealthy so he connected a filter to his exhaust vent.
    The problem is that he connected the exhaust vent to the blower on the roof of his apartment building.

    The blower is way too powerful, when you stand in his tent you can feel actual breeze from the airflow as the blower sucks all the air from the tent,
    enough to make the plants sway without a oscillating fan.

    He is about to enter the flower phase and he is afraid his filter will not be sufficient.
    The exhaust duct is 5", and his filter is rated for 16,000 CFM
    (it was the largest one available for this diameter).


    1. Can someone recommend a way to reduce the airflow so no odor will leak out?
    (For example, will clogging half the duct with tape change the volume of air, or will just increase the pressure?)

    2. Will adding smaller filters that will filter circulating air in the attic to reduce the load from the big filter help at all?
    (He has 2 duct fans rated to 5000 cfm with matching 5000cfm filters, he thought to just let them run inside the tent)

    3. How can we measure the current airflow to know what is the blower rating
    (we have no physical to the blower, it's in the machine room on the roof).

    Many thanks!
    Must be a giant ass filter 16,000 cfm.....something not right here

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    M_C (19-02-17)

  4. #3

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    Quote Originally Posted by SirBudsAlot View Post
    Must be a giant ass filter 16,000 cfm.....something not right here
    It's about 4' long and 1' in diameter and weighs about 20 lbs.
    So yeah it's quite big.

  5. #4
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    Quote Originally Posted by BananaLizard View Post
    It's about 4' long and 1' in diameter and weighs about 20 lbs.
    So yeah it's quite big.
    Shoot, how many plants is he growing to need something that large?

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    Still don't make any sense my 6 inch filter is 16lbs easy and it don't take no 16,000 cfm to pull thru it

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    ggotch (19-02-17)

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    Quote Originally Posted by The Aspie Toker View Post
    Shoot, how many plants is he growing to need something that large?
    He is only growing 5 at the moment,
    but he bought the largest filter he could find because the of this blower that sucks all the air out of his attic.
    He doesn't want any smell to leak out.

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  10. #7

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    Quote Originally Posted by SirBudsAlot View Post
    Still don't make any sense my 6 inch filter is 16lbs easy and it don't take no 16,000 cfm to pull thru it
    It's at least 50% heavier than yours, and probably much larger.
    Plus, It's not only about the amount of carbon in it, but mostly surface area for the carbon to work.

    It wasn't bought from a grow shop, it was bought from a chemical lab equipment supplier.
    I will buy mine from there too. The nice thing about it is that it's refillable, so after 1 year He can just buy activated carbon
    which costs nothing, and refill it.

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    Either way I would still appreciate if anyone has an answer to one or more of the 3 questions I posted:

    Quote Originally Posted by BananaLizard View Post
    1. Can someone recommend a way to reduce the airflow so no odor will leak out?
    (For example, will clogging half the duct with tape change the volume of air, or will just increase the pressure?)

    2. Will adding smaller filters that will filter circulating air in the attic to reduce the load from the big filter help at all?
    (He has 2 duct fans rated to 5000 cfm with matching 5000cfm filters, he thought to just let them run inside the tent)

    3. How can we measure the current airflow to know what is the blower rating
    (we have no physical to the blower, it's in the machine room on the roof).

    Many thanks!

  12. #9

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    lol,five plants my arse..

    nobody buys waay oversized commercial equipment for a home grow.

    two 5000cfm fans.n a four foot long filter. up in the machine room.. fk off

    in the roof of that factory you mean

  13. #10

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    Quote Originally Posted by ggotch View Post
    lol,five plants my arse..

    nobody buys waay oversized commercial equipment for a home grow.

    two 5000cfm fans.n a four foot long filter. up in the machine room.. fk off

    in the roof of that factory you mean
    Sorry, you guys were correct, my mistake!
    It's rated 16000 and 5000 cubic feet per HOUR, not per minute.
    the correct numbers will be : 260 cfm and 82cfm respectively!

    Apologies.

    Also I realized this would be better answered in the ventilation section.
    If a moderator can move it there I would be grateful!

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    ggotch (19-02-17)

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