Exhaust fan selection criteria for workshops

<Is it there an equation to decide the required number of exhaust fans?>

UK Building Regulations determine the provision of fans and their flowrates, so in the first instance a telephone call to the local authority's Planning Office might be a good move. A bathroom and an utility/laundry room would be good candidates, given there is a fair chance of water vapour being generated in those areas. The Planning Office will also be able to advise on whether a formal Planning Application is needed to satisfy local consents.

Usually the exhaust fan you are looking for is to provide number of air change.

To do so, see the capacity ex.fan m^3mtr / hrs

The require number of Air change per Hrs. work out no of ex.fan

Number of exhaust fans required is usually determined by code requirements, pollution control regulations, and common sense economics of operation and installation costs.

Exhaust fan sizing can be determined by code, by equipment requirements, or by cooling effect desired.

Some codes will require a fixed CFM per toilet, water closet, janitor's closet, etc.

Some equipment will list a specific air flow rate for exhaust, or certain dust producing operations may require an appropriate exhaust to keep a space clean. Hoods can be used to improve contaminant capture and reduce the required exhaust rate.

Exhaust rate for cooling can be determined from the simplified equation: cfm=BTU/1.1*ΔT(Fahrenheit).

My pet peeve in critiquing other exhaust system designs is the lack of understanding the effect of air pressure losses and static pressure on fan performance. Many exhaust fans do not have the power to move the required amount of air.