Understanding CFM (speed controllers)

OldMedUser said:

Exactly what I spoke about.

You have a totally different grow scenario and can't project your particular solutions onto another different situation.

My odor control is far from perfect. During the winter here we get totally dead air when it's -30C outside. My exhaust air exits under my shop and just flows across the yard. When I've grown stinky strains it's so f'n obvious that I'm growing pot. We don't have skunks up here in northern Alberta so I can't blame them like I used to do back in the Fraser Valley in BC.

The wife sells eggs so we have all sorts of strangers driving in to my small acreage, Talk about being paranoid!

I got a med card for 8g/day but I'm not legal for a single plant. Up here in Bumf**k Alberta the local cops would rip my place apart if they thought I had a single plant growing and I have 9 mom's vegging with at least 18 new plants about to sprout. Want to take around another 18 or more clones from the moms to get my breeding program in high gear. CBD everything! lol

It's not you or anyone in particular but the general lack of consideration for basic polite social intercourse that pervades this forum. If I had to point a finger it would be at the Admin/Owner. As I said I'm an Admin at another pot forum and I'd be slapping warning points on a lot of posters that hijack threads with trivial fights. Time outs next and bans after that. A lot of posts I see around here would get bans right off but seem to get ignored by Admin. I'm no rat so don't go reporting on anything that's not purely spam.

We have downvotes along with the upvotes which would go a long way to curtail thread bashing here but no such luck.

If what I said in a post got me a lot of unlikes I'd likely be more prudent about my future posts.

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So you bash what I have to say based on my environment, because your environment is differant... jesus man your a wealth of info...
Enjoy your half ass odor control, and not using fans for temp control. Your advise is super relevant and helpful.

I kinda wish @OldMedUser would stick to the forum he likes better, or at least followed his own advice. Reading his posts is like a example of what irony means.

omu is closer to being right than most of the rest of you.
you want your filter to be rated higher than your fan, that way you CAN'T run it too fast.
if you buy a decent fan and controller, you can run it at 10% and it doesn't make any noise. the lower you run the fan, the less noise it makes.
you want to figure out how many cfm you need to keep your temps where you want them, buy a fan capable of at least 25% more than you think you need, and a filter that is capable of at least 50% more than you need.
if you keep your prefilter washed weekly, a quality filter ought to last you at least 18 months, maybe 24, depending on the humidity

growingforfun said:

Just as I figured... cheap bulbs as well. Your focused on the minimum.
Do yourself a favor an get yourself a brand new hortilux super hps an compare the results.

When doing the minimum you'll get by. When you adjust your standards your results will reflect that.

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BAHAHA...I have. Like you I wasted tons of cash on hype and shit you really dont need. I know better now and I can still hit a gram per watt with cheap bulbs.

OldMedUser said:

None of this mis-information is helpful to a newer grower or anyone else for that matter.

So many threads are messed up by basically wrong information generating more wrong information.

Kind of an endless loop of thread hijacking.

You all might be right for YOUR particular grow environment but in this thread we are dealing with somebody elses unique environment so fighting about particulars just confuses the issue and is worse than no help at all.

I've been a member of many forums for a decade and a current Admin of one. This is the only forum where I see so much controversy about so much trivial crap.

"Best to remain silent and be thought an idiot than speak up and remove all traces of doubt."

Or as my old man used to say. 'If you got nothing useful to say then don't say nothing'

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So please grace us with your wise words of advice..other than get a filter thats bigger than needed...which isnt bad advice but nobody was contending either.

fridayfishfry said:

With carbon filters the slower the better so that means 400CFM is the max and 35% is OK.

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That is and isn't true.

For instance, some filters may be labeled 400 CFM but they advertise a 98.9% filtration rate @ only 180 CFM.

More expensive filters are actually built to be run @400 CFM flow and actually get the same effective filtration at that rate, so running slower would do you no good at all.

It's a lot like the debacle that is LED lighting. You really have to read the fine print to figure out what rate you SHOULD be running with any given filter.

redi jedi said:

So please grace us with your wise words of advice..other than get a filter thats bigger than needed...which isnt bad advice but nobody was contending either.

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As a chemist that worked in a hazardous waste facility one of my first jobs was evaluating the equipment in the new facility they build and reporting on deficiencies I found. I was in charge of the hydrocarbon disposal area and quite a few of he deficiencies I reported on dealt with the air filtration systems. At the time I was going thru blueprints and construction plans before the equipment was installed.

They ignored most of my recommendations as most would cost a bit more. They ended up paying a lot more ripping out the inadequate gear they installed. There's a hell of a lot of old boy's club crap going on in the background when a multi-million dollar facility is being built and I'm sure I stepped on a lot of toes. For example the guy they put in as head chemist was fresh out of university with a degree in chemical engineering. Never had a real job in his life but he was the manager's nephew and also fresh out of Iran. He was responsible for over a half dozen plant evacuations in the first 3 months of operation. As we were in a heavy industrial park these evacuations cause many other plants to close down and evacuate with us until they got the all-clear.

My whole area was all explosion proofed. At the old plant, a warehouse, we had many minor incidents and one huge explosion that luckily didn't result in any deaths tho one chemist lost an eye and hearing in one ear. That was caused by another uni taught inexperienced chemist adding acetone to a reaction vessel vented thru a sub-standard fan system. He thought it was just an acidic sol'n and as our current process generated a strong caustic with a lot of heat it seemed ok. I wasn't wearing my respirator when he dumped that 5gal pail into the fresh water we where adding to our vessel to start a new batch and I got a whiff of acetone. The other inexperienced uni chemist lifted his respirator to take a sniff and figured it was nothing. He's the guy that lost an eye.

Long story short, a larger carbon filter than your system really needs will do a better job for a lot longer that one equally matched to your stated fan throughput. A 400cmf fan will likely only pull around 300cfm thru a brand new filter rated at 400. How it preforms as time goes on has so many variables. Surface area of intake, depth of charcoal, porosity of charcoal, quality of the charcoal, how much stink your plants put out, number of plants etc etc.

For most of us our noses are crappy testing instruments. In the oil patch they use hydrocarbon sniffers to test for leaks and spills. One of those would be great for testing the output from a grow room exhaust. Get some real numbers over time instead of guesstimating.

OldMedUser said:

None of this mis-information is helpful to a newer grower or anyone else for that matter.

So many threads are messed up by basically wrong information generating more wrong information.

Kind of an endless loop of thread hijacking.

You all might be right for YOUR particular grow environment but in this thread we are dealing with somebody elses unique environment so fighting about particulars just confuses the issue and is worse than no help at all.

I've been a member of many forums for a decade and a current Admin of one. This is the only forum where I see so much controversy about so much trivial crap.

"Best to remain silent and be thought an idiot than speak up and remove all traces of doubt."

Or as my old man used to say. 'If you got nothing useful to say then don't say nothing'

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what the hell are u talking about
the info i gave was spot on .....using a carbon filter at less power then it is rated for is dumb and dangerous if u are in a area where growing is still a no no
the rest of the info can be verified simplly by looking at some fan

please before u say something like this check your facts ....i do

@OldMedUser
Hard to tell but this kinda looks like this forums equivalent of a down vote.

Your long winded off topic stories never actually help your point, they only prove to show you think nobody else has done things you have. Sorry bro.. your wise man on a hill bit isnt that good.

justugh said:

what the hell are u talking about
the info i gave was spot on .....using a carbon filter at less power then it is rated for is dumb and dangerous if u are in a area where growing is still a no no
the rest of the info can be verified simplly by looking at some fan

please before u say something like this check your facts ....i do

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He admitted he doesnt use the fans for cooling, and he doesnt have good odor control. His comments are not at all on topic, and the are bad information to anyone trying to clean the air or use air to cool their space. Hes getting 63f intake air in the summer. Something very few people have the luxury of. A RARE CASE.

growingforfun said:

He admitted he doesnt use the fans for cooling, and he doesnt have good odor control. His comments are not at all on topic, and the are bad information to anyone trying to clean the air or use air to cool their space. Hes getting 63f intake air in the summer. Something very few people have the luxury of. A RARE CASE.

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again i do not see where my advice and info is misleading or wrong
1 carbon filter designed to work one way at full power ....and the reason why
2 a link to a place that sells refillable active carbon filter (any size or CFM needs plus 50 extra bucks in pocket on next years replacement)
3 a break down of fan speeds to make shopping and choices quick (booster and inline defined )

guy before me explained the CFM how to measure it (personally i like over kill so i exchange every 1min )

as for his temps that is avg (u want to run a indoor grow off peak energy hours to reduce overhead cost for a better selling price)
i am from maryland and now in oregon night time temps are about 53 to 67


the only other info i would include with the info u relayed
1 u best build a powered filter intake box with a lvl 10 filter (hospital grade will stop bugs smoke pollen mold spores) temps of 65 in areas with water PM can wreck the crop

2 cooling for a grow area is best done 1 of 2 ways combined to number 3 and 4 for the finally tweak control
A mini split it is a actual room.....if have the money get a dual head with single compress slight over size (save u on money with prolonged life)
B if a tent system the air in the room it is needs to be cooled and RHed before it sucked in so a over power window shaker can do the job

3BTU on acs.......HIDs 1000w open hood needs 4000btus per light 1000w cooltube with venting outside needs 2000btus per light .......LEDs 1500-900w design 2000btus per light 600-300w 1000btus per light

4 cleaning air is simple there is a method called Air Polishing it is basically a carbon filter hooked up in the grow area but it returns the air back into the grow area instead of ejecting it .........the set up is simple to get 4 benefits for this
A the carbon filler is set on the ground (far point away from the air intake point ....pull the cool air deep in )
B u run the ducking to right above the light so the air flows down over the light (cooling the light and prolonging the life any electronics).......the carbon filter going out needs to be off set some does not heavy drawl on the down blow (i just increased the height some and moved it to back side of tent instead above the light)
C the last thing because of this u have made a cycle for the CO2 gas that has collected to mover down over the plants in a semi halo effect ....and u caused different air move ments to spread the gas into the plants
D this will cool the grow area down make it more stable temp .......if u do need lower temps u can increase the AC more or u can increase the speed of the exhaust fan

and a bonus tip with a powered intake u have some ducting u can play with .......get a 3/4 full paint can...... get some pine fur strip from home depot(98 cents for 8 feet).....cut the food about 4 feet or 5 ...take the wood and duct tape it to the side of a paint can making a stand ......a 6 inch fan clipped to it and run the ducting from powered intake to right behide so it blows air over the top of the plants cooling the IR heat that HID/LEDs

the only other part is Passive intake ....super simple
it works by doubling the size of the fan
4 inch fan would be a 8x8 hole
6 inch fan would be a 12x12 hole
and so on up to 12 ..........it does not have to be just one hole it can be several u just want the numbers to add up to at least that (this way it avoids needing to suck in from other cracks ....spores and dust collected in them going slow over the years if u change it can kick up some stuff for a few months)


that should answer any ? on venting and cooling a grow room

justugh said:

again i do not see where my advice and info is misleading or wrong
1 carbon filter designed to work one way at full power ....and the reason why
2 a link to a place that sells refillable active carbon filter (any size or CFM needs plus 50 extra bucks in pocket on next years replacement)
3 a break down of fan speeds to make shopping and choices quick (booster and inline defined )

guy before me explained the CFM how to measure it (personally i like over kill so i exchange every 1min )

as for his temps that is avg (u want to run a indoor grow off peak energy hours to reduce overhead cost for a better selling price)
i am from maryland and now in oregon night time temps are about 53 to 67


the only other info i would include with the info u relayed
1 u best build a powered filter intake box with a lvl 10 filter (hospital grade will stop bugs smoke pollen mold spores) temps of 65 in areas with water PM can wreck the crop

2 cooling for a grow area is best done 1 of 2 ways combined to number 3 and 4 for the finally tweak control
A mini split it is a actual room.....if have the money get a dual head with single compress slight over size (save u on money with prolonged life)
B if a tent system the air in the room it is needs to be cooled and RHed before it sucked in so a over power window shaker can do the job

3BTU on acs.......HIDs 1000w open hood needs 4000btus per light 1000w cooltube with venting outside needs 2000btus per light .......LEDs 1500-900w design 2000btus per light 600-300w 1000btus per light

4 cleaning air is simple there is a method called Air Polishing it is basically a carbon filter hooked up in the grow area but it returns the air back into the grow area instead of ejecting it .........the set up is simple to get 4 benefits for this
A the carbon filler is set on the ground (far point away from the air intake point ....pull the cool air deep in )
B u run the ducking to right above the light so the air flows down over the light (cooling the light and prolonging the life any electronics).......the carbon filter going out needs to be off set some does not heavy drawl on the down blow (i just increased the height some and moved it to back side of tent instead above the light)
C the last thing because of this u have made a cycle for the CO2 gas that has collected to mover down over the plants in a semi halo effect ....and u caused different air move ments to spread the gas into the plants
D this will cool the grow area down make it more stable temp .......if u do need lower temps u can increase the AC more or u can increase the speed of the exhaust fan

and a bonus tip with a powered intake u have some ducting u can play with .......get a 3/4 full paint can...... get some pine fur strip from home depot(98 cents for 8 feet).....cut the food about 4 feet or 5 ...take the wood and duct tape it to the side of a paint can making a stand ......a 6 inch fan clipped to it and run the ducting from powered intake to right behide so it blows air over the top of the plants cooling the IR heat that HID/LEDs

the only other part is Passive intake ....super simple
it works by doubling the size of the fan
4 inch fan would be a 8x8 hole
6 inch fan would be a 12x12 hole
and so on up to 12 ..........it does not have to be just one hole it can be several u just want the numbers to add up to at least that (this way it avoids needing to suck in from other cracks ....spores and dust collected in them going slow over the years if u change it can kick up some stuff for a few months)


that should answer any ? on venting and cooling a grow room

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I'm not saying your wrong. I'm saying the guy talking shit on both us of, is actually full of shit.

growingforfun said:

I'm not saying your wrong. I'm saying the guy talking shit on both us of, is actually full of shit.

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oh my bad i thought something completely wrong

if ever see in person owe a beer

i look at this way we were taught right doing our jobs to pass on the correct info ......i give my personal debt maybe 3 4 years after that i will stop tring (not many ppl come up with something have not seen or heard .......all ppl going legal and doing for own self )

miss the days of underground bunkers in ireland that was a fun design

OldMedUser said:

As a chemist that worked in a hazardous waste facility one of my first jobs was evaluating the equipment in the new facility they build and reporting on deficiencies I found. I was in charge of the hydrocarbon disposal area and quite a few of he deficiencies I reported on dealt with the air filtration systems. At the time I was going thru blueprints and construction plans before the equipment was installed.

They ignored most of my recommendations as most would cost a bit more. They ended up paying a lot more ripping out the inadequate gear they installed. There's a hell of a lot of old boy's club crap going on in the background when a multi-million dollar facility is being built and I'm sure I stepped on a lot of toes. For example the guy they put in as head chemist was fresh out of university with a degree in chemical engineering. Never had a real job in his life but he was the manager's nephew and also fresh out of Iran. He was responsible for over a half dozen plant evacuations in the first 3 months of operation. As we were in a heavy industrial park these evacuations cause many other plants to close down and evacuate with us until they got the all-clear.

My whole area was all explosion proofed. At the old plant, a warehouse, we had many minor incidents and one huge explosion that luckily didn't result in any deaths tho one chemist lost an eye and hearing in one ear. That was caused by another uni taught inexperienced chemist adding acetone to a reaction vessel vented thru a sub-standard fan system. He thought it was just an acidic sol'n and as our current process generated a strong caustic with a lot of heat it seemed ok. I wasn't wearing my respirator when he dumped that 5gal pail into the fresh water we where adding to our vessel to start a new batch and I got a whiff of acetone. The other inexperienced uni chemist lifted his respirator to take a sniff and figured it was nothing. He's the guy that lost an eye.

Long story short, a larger carbon filter than your system really needs will do a better job for a lot longer that one equally matched to your stated fan throughput. A 400cmf fan will likely only pull around 300cfm thru a brand new filter rated at 400. How it preforms as time goes on has so many variables. Surface area of intake, depth of charcoal, porosity of charcoal, quality of the charcoal, how much stink your plants put out, number of plants etc etc.

For most of us our noses are crappy testing instruments. In the oil patch they use hydrocarbon sniffers to test for leaks and spills. One of those would be great for testing the output from a grow room exhaust. Get some real numbers over time instead of guesstimating.

Click to expand...

Needing X air exchanges per minute is not bullshit. You cant achieve negative or positive pressure without the right amount of airflow. The nuclear power plant I worked at uses negative pressure to prevent contamination from leaving the reactor building. Hospitals use positive pressure in the burn wards to prevent germs from entering that ward. So please tell me how this is bullshit?

redi jedi said:

Needing X air exchanges per minute is not bullshit. You cant achieve negative or positive pressure without the right amount of airflow. The nuclear power plant I worked at uses negative pressure to prevent contamination from leaving the reactor building. Hospitals use positive pressure in the burn wards to prevent germs from entering that ward. So please tell me how this is bullshit?

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Dont waste your time, he does this in every thread I see him in.
He thinks hes so much smarter than everyone but forgets 3 year college really isnt much... I've got double that myself an im betting many others around here have several years.

He said he doesnt use the airflow for cooling, and he doesnt have proper odor control. Why he thinks he needed to join this thread I'll never know.
I can only hope @OldMedUser reads his own posts and takes the same advise he gave behavior wise, and maybe even just sticking to the forum he likes.

No need to slum it here with us.

fridayfishfry said:

With carbon filters the slower the better so that means 400CFM is the max and 35% is OK.

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Straightforward; thank you.

redi jedi said:

IIRC the most you can reduce speed is 50%...the fan will start making growling noises below that. If you need to reduce that much, the fan is oversized for the job.

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Hyper fans include a speed controller that reduces as low as 35%. I was just concerned that running it this low could put strain on the fan.

growingforfun said:

For some reason its popular on the forum right now to underpower fans. I disagree strongly with this trend.
Try to match your fan cfm to your filter, and use the largest ones you can at all times. For a 4x4x7 tent I always use a 8 inch fan that moves about 750 cfm. That's matched to a 750 cfm carbon filter. You'll have to find what works best for you, but when it comes to air movement and odor control I think its risky to do the minimum

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Fair point on using underpowered fans but they're quiet and save energy. It's a stretch to say if they really are underpowered for the filters when understanding how the filter's CFM is rated.

My 2x4x7 area only needs to move 18cfm-56cfm. The 6" Hyper Stealth fan moves 110cfm at 35% . This fan only consumes 35 watts at full power (moving 315cfm). I'd be comfortable using this set up in any space up to 4x8x8. It would still be effective at 75% on the dial .

Fans run more often than lights so it's important to research their energy consumption .

These are popular 8" fan specs




Taking it a step further to save energy.. I've considered running two carbon filters on one fan. For example using the same 6" Hyper fan rated at 315cfm to clean two 4" 200cfm filters. Using all 6" ducting, a 6" Y split, and 6" to 4" reducers connected directly to the filters. I'd be able to filter two tents from 2x4x7' up to 5x5x8' with a single fan (drawing only 35 watts).

TacoMac said:

That is and isn't true.

For instance, some filters may be labeled 400 CFM but they advertise a 98.9% filtration rate @ only 180 CFM.

More expensive filters are actually built to be run @400 CFM flow and actually get the same effective filtration at that rate, so running slower would do you no good at all.

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Thanks for sharing. This is a Phresh filter rated 400 CFM. I couldn't find a minimum recommendation to run this filter's fan.

fujiyama said:

Straightforward; thank you.

Hyper fans include a speed controller that reduces as low as 35%. I was just concerned that running it this low could put strain on the fan.

Fair point on using underpowered fans but they're quiet and save energy. It's a stretch to say if they really are underpowered for the filters when understanding how the filter's CFM is rated.

My 2x4x7 area only needs to move 18cfm-56cfm. The 6" Hyper Stealth fan moves 110cfm at 35% . This fan only consumes 35 watts at full power (moving 315cfm). I'd be comfortable using this set up in any space up to 4x8x8. It would still be effective at 75% on the dial .

Fans run more often than lights so it's important to research their energy consumption .

These are popular 8" fan specs

Taking it a step further to save energy.. I've considered running two carbon filters on one fan. For example using the same 6" Hyper fan rated at 315cfm to clean two 4" 200cfm filters. Using all 6" ducting, a 6" Y split, and 6" to 4" reducers connected directly to the filters. I'd be able to filter two tents from 2x4x7' up to 5x5x8' with a single fan (drawing only 35 watts).

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You can think all of that is true, that bla bla bla is "good enough"
People could smell my house from blocks away when I was using a single phresh filter 8x39 for a 8x8 room with a 8 inch fan.
Math is one thing. Dank ass bud doesnt care about math. Its something else entirely.

fujiyama said:

Thanks for sharing. This is a Phresh filter rated 400 CFM. I couldn't find a minimum recommendation to run this filter's fan.

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That's because there isn't one.

Phresh is a good brand. I'm assuming you have the 701005 model. That model is rated to be effective at 400 cfm. Anything above that lowers the effectiveness of the filter and will typically trigger the bypass valve. Anything below that will still be filtered, but not necessary more effectively.

So crank it up, move the air and you're fine. There's no reason to slow down your air flow with that filter.

growingforfun said:

You can think all of that is true, that bla bla bla is "good enough"
People could smell my house from blocks away when I was using a single phresh filter 8x39 for a 8x8 room with a 8 inch fan.
Math is one thing. Dank ass bud doesnt care about math. Its something else entirely.

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Will be keeping this in mind ..

TacoMac said:

That's because there isn't one.

Phresh is a good brand. I'm assuming you have the 701005 model. That model is rated to be effective at 400 cfm. Anything above that lowers the effectiveness of the filter and will typically trigger the bypass valve. Anything below that will still be filtered, but not necessary more effectively.

So crank it up, move the air and you're fine. There's no reason to slow down your air flow with that filter.

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Yes, Phresh 701005. Thanks for your input. I run around 50% to control the negative pressure and keep sound down (it's a big fan for this area). It's also cheaper on electricity but if smell becomes an issue I will crank it up.