Fan-Filter Matching

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noodleman

Active Member
It seems to me to be common knowledge that a fan outflow shouldn’t be greater than the rated capacity of the filter it’s attached to, and that it’s even better to have the fan less than the filter. I have never seen the topic mentioned anywhere, however, as to how far below the filter rating the fan can be set before there’s not enough oomph for the discharged air to get through the filter.

In my case I’m trying to redeploy a never used 400 cfm filter from old grows into a new smaller tent with a volume of 35 cu ft. A 350 cfm fan setting would result in ten exchanges of air a minute. I may want to slow the fan down more. How low could I go before the fan-filter system started to malfunction? I've never thought about this question before and I hope it’s of interest to other hobbyists.
 
jondamon

jondamon

Well-Known Member
noodleman said:
It seems to me to be common knowledge that a fan outflow shouldn’t be greater than the rated capacity of the filter it’s attached to, and that it’s even better to have the fan less than the filter. I have never seen the topic mentioned anywhere, however, as to how far below the filter rating the fan can be set before there’s not enough oomph for the discharged air to get through the filter.

In my case I’m trying to redeploy a never used 400 cfm filter from old grows into a new smaller tent with a volume of 35 cu ft. A 350 cfm fan setting would result in ten exchanges of air a minute. I may want to slow the fan down more. How low could I go before the fan-filter system started to malfunction? I've never thought about this question before and I hope it’s of interest to other hobbyists.
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Depends how old the filter is and what brand??

Cheapo no name filters are generally good for 9-12 months with their rated airflow through them.

Branded filters with good carbon beds can last circa 2-3 years with correct care and maintanence.

My filters are always rated with higher airflows than my fan.

Currently use a 250CFM fan with a 450CFM filter.



J
 
jijiandfarmgang

jijiandfarmgang

Well-Known Member
noodleman said:
It seems to me to be common knowledge that a fan outflow shouldn’t be greater than the rated capacity of the filter it’s attached to, and that it’s even better to have the fan less than the filter. I have never seen the topic mentioned anywhere, however, as to how far below the filter rating the fan can be set before there’s not enough oomph for the discharged air to get through the filter.
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Well.....not so fast.

Kind of depends on what type of filter your talking about. I haven't seen a rating on HEPA filters, but you are supposed to undersize them......but I'm thinking your talking about carbon filters.

The larger carbon filters don't have more of a restriction they have less. So inifinity I guess?

- Jiji
 
ficklejester

ficklejester

Well-Known Member
The fan won't malfunction but you'll want one that will adjust speed based on voltage. You can run it as low as you want as long as you're removing air faster than it's being brought in the room- to ensure negative pressure. The less air coming in, the less oxygen and CO2 will be available to your plants, though. I've read recommendations of recycling air every 5 minutes in a contained grow space, though I try to stay under 2 minutes or better.
 
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noodleman

Active Member
Thanks for all the input. I have a 6"x16" Phresh filter that I believe is rated at 400 cfm, and a 6" 400 cfm fan. I may get an 8" Vortex S series fan (about 700 cfm) though to replace the smaller fan, and then reduce its flow by 50% or more, and connect it to the 6" filter with an adapter. I've got to have a quiet operation because the tent will be in a closet near the center of my apartment, and I thought an 8" running at half speed would be quieter than a 6" running near full speed. I also may want to crank the fan up higher to create more negative pressure when I open the tent for maintenance so smells won't escape. I need to have a very stealth operation.

My basic question was how low can I set the fan attached to my 6" and still maintain adequate flow through the filter so that negative pressure is maintained in the tent. Based on Jondamon's experience I would guess I could bring my fan down to 250 - 300 cfm.
 
jijiandfarmgang

jijiandfarmgang

Well-Known Member
Don't get a an 8" fan for 35 cu ft

Most fan manufacturers don't recommend going under 50 percent power (contact manufacturer before you try this)

- Jiji
 
ficklejester

ficklejester

Well-Known Member
noodleman said:
My basic question was how low can I set the fan attached to my 6" and still maintain adequate flow through the filter so that negative pressure is maintained in the tent. Based on Jondamon's experience I would guess I could bring my fan down to 250 - 300 cfm.
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Look for suction- when you close the door it should pull itself shut a little, if it's not too heavy. You can also blow a little smoke near intake areas and it should be sucked in.
 
jondamon

jondamon

Well-Known Member
noodleman said:
Thanks for all the input. I have a 6"x16" Phresh filter that I believe is rated at 400 cfm, and a 6" 400 cfm fan. I may get an 8" Vortex S series fan (about 700 cfm) though to replace the smaller fan, and then reduce its flow by 50% or more, and connect it to the 6" filter with an adapter. I've got to have a quiet operation because the tent will be in a closet near the center of my apartment, and I thought an 8" running at half speed would be quieter than a 6" running near full speed. I also may want to crank the fan up higher to create more negative pressure when I open the tent for maintenance so smells won't escape. I need to have a very stealth operation.

My basic question was how low can I set the fan attached to my 6" and still maintain adequate flow through the filter so that negative pressure is maintained in the tent. Based on Jondamon's experience I would guess I could bring my fan down to 250 - 300 cfm.
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The biggest question of all is if you'll need to crank up a fan with higher CFM than the filter?

If you do have to crank up say a 700CFM fan attached to a 400CFM filter kiss goodbye to your carbon scrubbers ability to remove the odours.

400cfm fan and filter will be fine even if you have to reduce your fans speed.

I would never buy a fan without making sure my filter was capable of at least the same CFM of the fan on max speed or I would buy I new filter to match it.


Unless I'm wrong have you mentioned your lighting choice yet?




J
 
N

noodleman

Active Member
Jondamon -

I have 2 Lumigrow 330's from earlier grows. I'll only be growing one 7 gallon or two 3 gallon plants at a time. I'll give them as much light as they need but I don't think I'll need both lamps running at full power. Maybe each lamp ratcheted down to 50% - 70% power will be good for my size grow, but I don't know for sure until I start. I'll be using a 2 x 2.5 x 7 ft Gorilla tent. I haven't grown anything for two years but fortunately I have a substantial stash remaining from my earlier days so I can afford to go methodically in planning the new set up. And It's possible I could be doing this legally soon, although I don't know if I'd bother to grow pot if I could openly buy the strains I like for $100/oz.

Thanks for everyone's help and interest. Happy and safe growing.
 
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noodleman

Active Member
sold777 said:
Nice I have 1 lumigrow and 1 prosource 180 and love them .
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I guess it's ok to hijack my own thread. About the lumigrow, I've only used them once in my last grow about 2 year ago. I had maybe 9 plants with the 2 330s and 864 watts of T5s. The T5s were pretty hot and I've ditched them since. I was wondering if you could give me an idea as to how hot just the 2 330s would be in a 2 x 2.5 x 7 ft. tent with an outside temperature of about 72 F. I'm planning to use my 6" fan dialed down to maybe 4-6 tent circulations per minute. Heat was a big problem with the T5s and I'm wondering what conditions will be like without them. Thanks your help. It's so great to have a venue for exchanging this kind of information.
 
sold777

sold777

Well-Known Member
noodleman said:
I guess it's ok to hijack my own thread. About the lumigrow, I've only used them once in my last grow about 2 year ago. I had maybe 9 plants with the 2 330s and 864 watts of T5s. The T5s were pretty hot and I've ditched them since. I was wondering if you could give me an idea as to how hot just the 2 330s would be in a 2 x 2.5 x 7 ft. tent with an outside temperature of about 72 F. I'm planning to use my 6" fan dialed down to maybe 4-6 tent circulations per minute. Heat was a big problem with the T5s and I'm wondering what conditions will be like without them. Thanks your help. It's so great to have a venue for exchanging this kind of information.
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Oo hijack your thread how have I don that your losing me
 
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