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Thread: Carbon filter size

  1. #1

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    Default Carbon filter size

    Quick question . I have a really big and strong extractor fan but a smaller Carbon filter . Does the size of the carbon filter change the amount of air your extractor fan can extract ? Ie if I put it on it blows out strong ,but if I get a 6in carbon filter double the size will my extractor fan pull out more

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  3. #2

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    Quote Originally Posted by Grow8369 View Post
    Quick question . I have a really big and strong extractor fan but a smaller Carbon filter . Does the size of the carbon filter change the amount of air your extractor fan can extract ? Ie if I put it on it blows out strong ,but if I get a 6in carbon filter double the size will my extractor fan pull out more
    Short answer, yes.

    Most filters have an extraction rate just like a fan does.

    If fan and filter are the same size the filter will down rate the extraction rate of the fan by 25%

    Sent from my SM-G981B using Tapatalk

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  5. #3

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    The stale smelly air need contact time with carbon in order for it do its magic....You need to match or exceed the size of the filter to the fan your using if you intend to run your fan at full speed...


    Regards BL

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  7. #4

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    Its important to match fan and filter flow rates.

    If the fan pulls too much air then as Bud says in the post above the filter won't have time to scrub the air clean. Also the filter can restrict airflow through the fan placing extra load on the motor and possibly shortening its lifespan.

    Running too large of a filter will cause the air to be pulled unevenly through the length of the filter. As air will take the path of least resistance more air will pass through the carbon near the fan than the carbon at the far end of the filter. This will cause the most used carbon to become clogged faster than normal and the rest of the carbon to be relatively clean. Your filter will lose effectiveness and smell will again become an issue requiring repacking of the carbon to be done more often.

    Personally I like to run oversize filters as a fresh filter with undersize fan I feel gives the cleanest air out. If I feel the top of the filter is starting to clog then I'll block the top third of the filter by wrapping gaffa tape round it forcing the air to be pulled from the lower still relatively clean section of the filter until it can be repacked at cropping time.
    Last edited by Muttz; 31-05-20 at 01:03 AM. Reason: typo

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  9. #5

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    Quote Originally Posted by Muttz View Post
    Its important to match fan and filter flow rates.

    If the fan pulls too much air then as Bud says in the post above the filter won't have time to scrub the air clean. Also the filter can restrict airflow through the fan placing extra load on the motor and possibly shortening its lifespan.

    Running too large of a filter will cause the air to be pulled unevenly through the length of the filter. As air will take the path of least resistance more air will pass through the carbon near the fan than the carbon at the far end of the filter. This will cause the most used carbon to become clogged faster than normal and the rest of the carbon to be relatively clean. Your filter will lose effectiveness and smell will again become an issue requiring repacking of the carbon to be done more often.

    Personally I like to run oversize filters as a fresh filter with undersize fan I feel gives the cleanest air out. If I feel the top of the filter is starting to clog then I'll block the top third of the filter by wrapping gaffa tape round it forcing the air to be pulled from the lower still relatively clean section of the filter until it can be repacked at cropping time.
    Nice one Muttz,
    So a 250 m3h carbon and exhaust would be
    As efficient as 200 m3h because they are the same size?

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  11. #6

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    I'm guessing that m3h is cubic meters per hour? I work in cfm or cubic foot per minute so forgive if my reply is generic. Also I'm not a venting expert, I just did my homework when I started out and was lucky enough to meet and toke with people that were.
    you asked
    "So a 250 m3h carbon and exhaust would be
    As efficient as 200 m3h because they are the same size? "

    I guess by "same size" you mean they are the same physical size and use the same size ducting? Although fans are normally described in our hobby by inches that's not really the important number, what is important is how much air it flows, the cfm/m3h. Ducting size can be stepped up or down with the right fittings, however 2 fans of the same bore or size will within reason flow more or less the same amount of air and that's why bore is a accepted way to describe a fan/filter.

    2 fans of the same bore might be described with different cfm for many reasons, the motor used, blade design, its intended use, eg downrated for use in long-life low maintenance or low noise applications or maybe the guy writing the sales broacher just got a bit cheeky to try and sell more fans. Most technical spec sheets will give a intended use range like 200 to 250 and that normally is what it will flow freestanding (250) or when in use and pulling through ducting and filters (200) a drop of 20% which seems realistic to me.

    so to answer your question of if a 250 is as efficient as a 200 of the same size then erm yeah I guess so, I mean considering that depending on make, intended use and how the spec sheet has been interpreted then they probably flow the same amount of air anyway. if however your looking at two fans from the same maker on the same web site of the same size but with different cfm then I'm guessing they have different intended uses and one or the other will have some reference to being high flow or low noise or long life, something along those lines.

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