little confuse on ventilation.. 5x CFM? or CFM /5?

So i've been doing a lot of research on ventilation lately getting ready to build my first cab and one thing ive been really confused about is the fan CFM requirements simply because people say 2 completely different things. A lot of stickies and common growing FAQs state that you want your air exchanged once every 3-5 minutes. Then to calculate in a little more headroom for ducts, filter, etc. Cool i get that. However a lot of people on the forums seem to be recommending fans rated for 5x the CF of their cabs AKA exchanging the air 5 times a mintue which seems a bit excessive. I'm going for a dead silent cab and i feel like exchanging air 5x a minute will create noticeable suction through the intake, also i hear plants in a vacuum is bad. So what's right? besides the sticky here i found another good reference but it's a little old, does this math seem legit? http://forum.grassci...-questions.html

Dead silent is going to be tough to obtain, but a great goal to work toward. Exchanging your air once every 5 minutes will do the trick. 5 times per minute would be a bit excessive, and quite noisy. The purpose of exchanging air is two fold:

1) co2 exchange. plants use co2 in their immediate surroundings, by exchanging air and circulating it with a fan, the plants will have access to an unlimited supply of co2 at normal atmospheric levels.

2) heat removal. Unless you're using A/C, you want to vent the warm air from your grow space, out the top of the enclosure, allowing fresh/cool air to refill the space, entering from the bottom.

Cool air coming in the bottom and exhausting the top is important. One, because hot air rises, (or cold air sinks) and two, the mechanism the plants use to intake co2 are located on the underside of their leaves. Air moving from the bottom up helps them use the co2 in a more efficient manner.

The ideal method is to use a fan to exhaust the inside air to outside of your grow space, not using a fan to pressurize the growspace. (fan should blow out, not in)

All that aside, you're gonna want a fan that's matched to the proper rating of your carbon filter.

I'd suggest using a duct booster 24/7, and then add a bigger fan on a thermostat that will exhaust when the grow space has reached a certain temperature (78f, unless you're using co2)

Dead silent is going to be tough to obtain, but a great goal to work toward. Exchanging your air once every 5 minutes will do the trick. 5 times per minute would be a bit excessive, and quite noisy. The purpose of exchanging air is two fold:

1) co2 exchange. plants use co2 in their immediate surroundings, by exchanging air and circulating it with a fan, the plants will have access to an unlimited supply of co2 at normal atmospheric levels.

2) heat removal. Unless you're using A/C, you want to vent the warm air from your grow space, out the top of the enclosure, allowing fresh/cool air to refill the space, entering from the bottom.

Cool air coming in the bottom and exhausting the top is important. One, because hot air rises, (or cold air sinks) and two, the mechanism the plants use to intake co2 are located on the underside of their leaves. Air moving from the bottom up helps them use the co2 in a more efficient manner.

The ideal method is to use a fan to exhaust the inside air to outside of your grow space, not using a fan to pressurize the growspace. (fan should blow out, not in)

All that aside, you're gonna want a fan that's matched to the proper rating of your carbon filter.

I'd suggest using a duct booster 24/7, and then add a bigger fan on a thermostat that will exhaust when the grow space has reached a certain temperature (78f, unless you're using co2)

Hows it goin man seems like your on your vent tip got a couple ?s if ya dont mind n not to b a dick but if could get back to me asap id appreciate

Ok first a dummy question(not really bout venting)
I have a 1000w ballast would I b safe to run 2 1000w bulbs on tht or would the bulbs jus put out 500 each?

Second
Ok first of all im workin with a 10x10x6.5 room, n like I said before I have 2 1000w bulbs and 2 vented hoods now would 2 of the 8in inline duct fans from htgsupply be sufficient in venting my room?and would 1 b sufficient if im only able to use one light an hood?

Last thing is how do I wanna set the venting up? Do i run air from the outside of the room through the light/s and then outside?and then would tht b all I had to do as far as venting or do I.need a whole other setup for the air in the actual room?

EDIT the inline fans are rated at 500cfm

Edited by iDonate, 03 July 2012 - 03:18 AM.

...pull your air from within your home, through your grow space, then vent outside....temps/rh are easier to control from within the home....the more air you move the better, bad airflow can lead to many problems , so you can't really over-do-it...just don't pull more air through your scrubber than called for.

Edited by trichome fiend, 03 July 2012 - 03:24 AM.