Calculating Exhaust Fan size

Ok I have a room that is 10'x11'x8'. I am trying to calculate the size of a fan I would need for my exhaust. I think I am doing it correctly but I want to get some feedback from you guys. I would just do LxWxH = A and A would be the CFM I would need correct? So 10x11x8= 880. So I would need a fan that has a CFM of 880?

Negatory. Well I am also not sure but I do see some flaws in your logic. Length x width x height = volume. You came up with an air flow of 880 cubic feet per minute. While 880 is the correct number of cubic feet in your room, that doesn't mean that you necessarily need to move that much air per minute. Im not sure how many CFM you need compared to the volume of the room.

Yeah I was thinking I was wrong. I heard that you need to replace the entire volume of air in the room every 5 minutes to exhaust efficiently. So would I go 880 divided by 5 which would equal 176...Maybe thats right lol

still wrong, sorry. you replace the air in the room every five minutes just to get fresh co2 to the plants. you can end up needing to exchange air much more, like twice a minute if you have severe cooling issues. best plan is to buy an oversized fan with a variable speed controller and then dial in your fan based on the needs of your specific situation.

okay so if the rule of thumb is to cycle the air every 5 minutes then I would say 176 is approx your number, I would go a higher just to be on the safe side. If heat is an issue then bump it up, or mount the fans more strategically to take the heat from the lights on out.

176 will not be near enough cfm if you are trying to cool the room. That is only the bare minimum for fresh air for the plants , not near enough to help cool the room .

OMG LS6 said:

Yeah I was thinking I was wrong. I heard that you need to replace the entire volume of air in the room every 5 minutes to exhaust efficiently. So would I go 880 divided by 5 which would equal 176...Maybe thats right lol

Click to expand...

When I installed mine I was told something about the division and multiplications but didn't know it was so complicated until I read your post or maybe my math is not so good at the moment.

Your room is 110.0 squarefeet, please review the three levels of reccomendation bellow suited to your grow room

Lighting
The minimum recommended lighting for your area is 2750 watts
Ventilation
The minimum flow rating of your fan should be 733.3 Cubic Feet per Minute (CFM)
Power Requirements
This setup will require 29.8 amps to be available at all times for safest operation*
Lighting
The optimum reccomended lighting for your area is 4400 watts
Ventilation
For optimum ventilation the flow rating of your fan should be around 806.7 Cubic Feet per Minute
Power Requirements
This setup will require 47.7 amps to be available at all times for safest operation* Lighting
The maximum reccomended lighting for your area is 6600 watts
Ventilation
Going this way you will require a fan with a flow rating of at least 953.3 Cubic Feet per Minute
Power Requirements
This setup will require 71.5 amps to be available at all times for safest operation*
Additional Comments
Getting to these points and or over it is highly reccomended the grower use Co2 in their room as your plants will only be able to photosythesise a certain amount of light before needing a Co2 boost to benifit

Here's a good article: http://urbangardenmagazine.com/2009/04/calculating-fan-requirements-for-your-indoor-hydroponic-garden/

But looks like cowell did all the work for you.