For Calculating The Exhaust Fan Capacity As per area

A little more information is required.

It depends on what you are trying to exhaust (eg. washroom facilities, kitchen, welding fumes, dust, ...............)

It also depends on the overall HVAC system you are dealing with - for example, if you already have conditioned the air (cooled/dehumidified) and/or scrubbed/filtered the air, then you will want to minimize the amount of air "lost".

So please provide some more information.

Just another comment - it also depends on your supply air - in some cases (such as in a control room of an industrial facility) you do not want to exhaust more air than is being supplied into the area or you will develop a negative pressure situation which will allow ingress of unwanted fumes.

It would also depend on the amount of dust or fumes you want to remove and how many air changes per minute you need to keep the area clean. Calculate the volume of the room and multiply it by the number of air changes per minute you need to have and you should get the CFM of the exhaust fan you need. Normally the exhaust pressure is very low, you only need the volume of air to be exhausted, not the pressure.

vshwn7@aol.com

Depending on where you are at and what you are doing, there might also be building codes to satisfy. Different locations require certain airflow rate per toilet, for example.

Rajiv,

As it stands, your question is meaningless:

Whole books have been written on the subject.

They boil down to knowing What you are dealing with, Why you are dealing with it, What you have to do with it, How are you going to handle it and What special factors are involved.

"What you are dealing with?" defines materials, point of discharge, safety precautions, calculation modifications and other provisions.

"Why you are dealing with it" defines environmental condition limits. For example, lets say you were exhausting toxic fumes from a work area to maintain a level of contamination below the "safe exposure limit" set for the chemicals you are exhausting, or If you are exhausting air to keep an area cool without air-conditioning, you would ask "How much air do I have to move to keep the space temperature below ____ degrees, assuming ____ degree intake air and ______ watts/Btuh heat generation".

"What do you have to do with it?" deals with where you can discharge it to, can you recover heat or cold from it. For example I once dealt with exhausting a chlorine room next to a children's play area at a pool. ("At grade" discharge was out.)

"How you are going to do it?" Physically how is your system set up, Will it use a large fan at low speed or a small fan at high speed? what type of fan: axial, centrifugal, propeller etc. (In the above chlorine room fan sizing had to take into account specific gravity (chlorine is heavier than air), room volume, estimated leakage rate, location of exhaust inlet (at floor), discharge location (30 feet above grade) disharge hood losses (keep rain out of exhaust duct) duct losses etc.)

"What Special Factors are involved?" Catch all category for everything that might affect your project that already wasn't covered above.

You need to provide more info. There simply is not enough info in your E-mail to properly frame your question let alone help you get an answer.