What size fan should i run?

[bluethumb]

I'm using a 70" (tall) by 30" (wide) by 20.5" (deep) closet.

I bought a 95CFM fan but i'm thinking this is too small. I have a 250watt HPS in there. With the light on its staying at a steady 90 degrees F. The fan wasn't running the whole time so i hope it goes down a bit in temp.

Did i get a fan thats way too weak? Its also hooked up to a carbon scrubber.

 

[badjha]


How to size your exhaust fan

"There are many calculations on the web for sizing a fan for ventilating grow rooms; however, what these calculations fail to take into consideration is the friction loss on carbon filters, increased temperatures from HID lights and CO2, etc. The following calculation can be used as a guide for sizing an exhaust fan for a growing area (keep in mind that this calculation will give you the lowest required CFM required to ventilate the grow room):

Step 1 – Room Volume
First the volume of the room needs to be calculated. To calculate multiply length x width x height of growing area e.g. A room that is 8' x 8' x 8' will have a volume of 512 cubic feet.

Step 2 – CFM Required
The fan should be able to adequately exchange the air in a grow room once every three minutes. Therefore, 512 cubic feet/3 minutes = 171 cfm. This will be the absolute minimum cfm for exchanging the air in a grow room.

Step 3 – Additional factors
Unfortunately, the minimum cfm needed to ventilate a grow room is never quite that simple. Once the grower has calculated the minimum cfm required for their grow room the following additional factors need to be considered:
Number of HID lights – add 5% per air cooled light or 10-15% per non-air cooled light. 

CO2 – add 5% for rooms with CO2 enrichment 

Filters – if a carbon filter is to be used with the exhaust system then add 20%

Ambient temperature – for hot climates (such as Southern California) add 25%, for hot and humid climates (such as Florida) add up to 40%."
i can't remember where did i find this info but i hope that will help

 

[JacuzziSplot]

for small spaces like cabinets and closets a good shortcut for for finding the airflow needed to keep temps within a few degrees above room temp (only works if room temps are between 60f-80f) is to multiply the wattage of your lights by 0.52. So for 250w you would need 130cfm. I did a shitload of calculations to come up with that number and it was mostly the ventilation 101 thread that got me to it.

But that number is the airflow with minimal ducting and no carbon filter. If you use a carbon filter and/or have bends in the ducting you need to add another 25%-30% or 170cfm in your case.