How Much Air Exchange Do you Need?

k folks, i have seen a lot of conflicting info on this site for the amount of air exchange you want when running a carbon filter in a grow room. i've seen anything from exchanging air once per 5 minutes to 5 times per minute. one end of that range has to be flat out wrong.

any help appreciated.

first source - "Two rules of thumb are to maintain an air flow that is eight to ten times the total volume of your vented space per hour, or, for indoor growing applications, 150 CFM per 1000 watt light bulb"; taken from How To Control The Smell Of Your Marijuana Plants Using Active Carbon Filters

Thanks for posting this desertrat! This is a definately a topic which needs some attention, I am right now trying to figure out my ventilation system and have also seen some conflicting information for equations to use...

I know you guys will be able to help! So lets hear it...

second source -"the goal is to exchange the air of the space every 5 min or less." from - Sealed growroom questions.. - Marijuana Growing

third source - "Hardcore favors charcoal filter odor control, augmented by in-line fans that are big enough to exchange all the air in the room in an hour" from The ultimate grow room

so from three sources we have:

once per hour
8 -10 times per hour
over 12 times per hour

still looking

Every one will give you a different number and they will be all about the same every 3min to every half hour depending on allot of variables.

There are two things to account for. Co2 and Heat

Hmm FAQ Time BRB

desertrat said:

third source - "Hardcore favors charcoal filter odor control, augmented by in-line fans that are big enough to exchange all the air in the room in an hour" from The ultimate grow room

so from three sources we have:

once per hour
8 -10 times per hour
over 12 times per hour

still looking

Click to expand...

and 20 times per hour from

-=4:20=-Guy said:

Every one will give you a different number and they will be all about the same every 3min to every half hour depending on allot of variables.

There are two things to account for. Co2 and Heat

Hmm FAQ Time BRB

Click to expand...

sure hope that math was right becaause i sure as shit am nont going to be able to check it

K check it out
https://www.rollitup.org/indoor-growing/105926-common-air-flow-requirements.html

added data from this thread to 420guys link below. he;s got a great chart for determining airflow requirements; please help here with input on air flow requirements for a carbon scrubber. so far we have a range of air exchange of once per hour to 20 times per hour.

so from three sources we have:

once per hour
8 -10 times per hour
over 12 times per hour
20 times per hour

and 600 times per hour ...............from https://www.rollitup.org/grow-room-design-setup/106245-500w-cfl.html this:
I have a 265cfm blower exhausting my 24 cuft box, so turns over 10 times a minute

Each fan has a rating that tells you how many cubic feet of air per minute (CFM) it will move. When dealing with above average temperatures you will want your fan to exchange the grow room air 3-5 times in one minute, so for a room that is 40 cubic feet, a fan that is capable of moving 120-200 cfm (cubic feet per minute) is recommended. If you only want to replace depleted levels of co2 and are growing in a closet using fluorescents, one room change per five minutes (divide room size by 5) will be adequate.

To calculate your room size, multiply Width by Length by Height, this will give you the CFM rating required for one room change per minute.

Air that’s exhausted will be replaced by fresh air, which is drawn from
Passive Intakes-
located opposite the exhaust at the floor of your grow room (Recommended for closet grows) or forced in using another blower (recommended for larger grow rooms).

For internal circulation oscillating fans are In my opinion the most efficient devices for circulating air in a room. The gentle back and forth sway of the fan is very beneficial for the developing plants. These fans tend to keep anaerobic moulds down by constantly freshening any potentially stagnant air. Home improvement centres carry a large array of various types and styles of air-moving fans, there are wall-mounted styles available and most are relatively inexpensive.

NOTE: To convert CFM to CMH use the folowing formula CFM X 0.03 X 60 = CMH

You have it right there. It really depends on your set up..

If you are running air cooled lights in a sealed system that is temp and co2 controlled you will need to exchange the air less often as you are simply replenishing co2 and not really cooling the room all that much as the lights are being run off a 2nd fan in a different loop. In a situation like that I still like to have 2x per minute which is pretty easy. Keep in mind that the filter cuts down the cfm of airflow a bit.

Just use an oscillating fan inside the room.


In one of my grows I have about 100 cf of space in each room and I use a can 33 combo with that. Rated at 265 cfm minus the filter you get about 225 cfm or 2.25 times per minute. It works great.

You know what man, lol i lied....the correct answer is about 20 times an hour or once every 5 minutes, just google "air exchange grow"

Is there any real information or studies out there on the amount of air exchange or ventilation needed for healthy growth?

I'm doing calculations on an insulated grow chamber for cold environments. It looks like heat loss through the insulation shouldn't be a problem, so that just leaves the heat loss through air exchange.

I've done some searching and the numbers are all over the place. Is it just a matter of keeping the C02 level high enough? Is oxygen build up a problem?
I know that with animals in a sealed room, the C02 rises to a poisonous level before the oxygen gets too low.

1212ham said:

Is there any real information or studies out there on the amount of air exchange or ventilation needed for healthy growth?

I'm doing calculations on an insulated grow chamber for cold environments. It looks like heat loss through the insulation shouldn't be a problem, so that just leaves the heat loss through air exchange.

I've done some searching and the numbers are all over the place. Is it just a matter of keeping the C02 level high enough? Is oxygen build up a problem?
I know that with animals in a sealed room, the C02 rises to a poisonous level before the oxygen gets too low.

Click to expand...

I go by is my fan exhausting fast enough to suck my door closed on my rooms if so that’s more than enough. If your pulling air that fast co2 will be exchanged and renewed ore than fast enough for your growing needs.

Granted it’s not scientific or anything

Its all about keeping CO2 available to the plants, and keeping temps appropriate. You can run a sealed room if you supplement CO2 and have temp controls.