CFM
- Thread starter TomTomMj
- Start date
coreywebster
Well-Known Member
The 4 " should do it. But if you want it quieter then run the 6" with a speed controller so you can turn it down. This also will make the filter last longer. Upsizing the filter will also mean you have to replace it less often and is also quieter running.
Fan speed controllers are not required but are useful, since you can lower noise, control temps better if it happens to be a bit too cool and prolong filter lifespan.
Don't buy a cheap filter.
I kind of repeated myself there but you get the gist.
Fan speed controllers are not required but are useful, since you can lower noise, control temps better if it happens to be a bit too cool and prolong filter lifespan.
Don't buy a cheap filter.
I kind of repeated myself there but you get the gist.
Wouldn't wrapping that end lower the cfm of the filter?
Owly
Member
Yes, that only makes sense to do if your filter is rated for 3X - 5X more air than you are actually using it for.
The big ones work out to be more economical and work better.
Roger A. Shrubber
Well-Known Member
if you feel handy, you can grind the rivets off and swap the end flanges around, re-attach with short machine screws, effectively doubling the useful life of your filter without slowing down the CFM. so if you buy the bigger one, flip when you notice it becoming less effective, you may get as much as 3 years out of one if you have a small grow
and i agree, bigger is better, always buy a filter rated for more cfm than your fan, that way you can't over-draw the fan, (pull air through it too quickly so the carbon doesn't have time to work), so if you have a 400 cfm fan, get a 500 or 550 cfm filter and you can't go wrong
and i agree, bigger is better, always buy a filter rated for more cfm than your fan, that way you can't over-draw the fan, (pull air through it too quickly so the carbon doesn't have time to work), so if you have a 400 cfm fan, get a 500 or 550 cfm filter and you can't go wrong
OutlawGrower
Member
Apply some common sense to it don't just make a guess. A 2x4x5 room is 40 cubit feet, you want to exchange all of that air at least every 50-60 seconds so you want at least a 50 cfm fan, and that means the fan is running at full speed which will create additional noise and use more power. If you get a fan with 100cfm you can run it at half speed and achieve the same result. You proably want to exchange your air more often than the bare minimum though, and if you attach an appropriate size carbon filter you can half the CFM of your fan, bigger filters breathe better than smaller filters due to larger surface area. I would get a minimum of the 6" 300+cfm fan which with a filter attached would be approx 150cfm and then you can run it at around half speed to get 75cfm which is still around double what you need for such a small area.
Awesome, thank you! Do you have an equation for an input fan incase there is too much negative air pressure?
OutlawGrower
Member
I'm far from an expert and don't have any equations, but for passive intake the general rule is twice as much intake as exhaust and if you want to add an input fan, just make it 50-75% of the cfm of the exhaust fan I think, which should create a nice amount of negative pressure. If you get speed controllable fans you can tweak it until you're happy. Remember that your environment will change constantly as your plants grow so you want to keep an eye on temps and humidity and ramp up the fan speed or slow it down to keep it just right. I'm new here but there is probably a stick or something somewhere which covers this.
Roger A. Shrubber
Well-Known Member
i've found that opening the bottom flaps on the tent is usually more than enough to keep from having too much negative pressure. really, the only way to have too much negative pressure is if it collapses your tent, negative pressure is good as long as its not sucking leaves off your plant and caving in your tent
But if it's sucking up all the air and not bringing in air quick enough, without a fan, is the plant getting enough fresh air?
Roger A. Shrubber
Well-Known Member
it aint a wind tunnel at JPL, its an exhaust fan. if its that powerful, turn it down.
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