Coverage area of a smoke removal system is the most common area where people are confused. Manufacturers and marketers of smoke removal systems contribute to this confusion by overstating the coverage area for their smoke eaters. As an indoor airquality specialist, this is the area where I am most helpful to my clients. While calculating the coverage area of smoke eaters is not an exact science, we are going to share with you some of the rules that we use everyday, when designing and configuring systems for our clients, which include many popular bars, restaurants, casinos, bowling alleys, bingo halls and our favorite… night clubs!
There are several factors to consider when sizing a smoke removal system:
1. Air changes per hour
3. Number of people / number of smokers
Air Changes per Hour
We usually try to meet or exceed 12 air changes per hour in most smoking applications. If you are trying to eliminate cigar smoke or if you are dealing with secondhand smoke, you should try to achieve 14 (or more) air changes per hour. To calculate airchanges per hour, you will need the measurements of the room or area you intend to cover and use the following equation:
In the below example, we will use a 2500 square foot room, with 9 foot ceilings and we will try to achieve 12 air changes per hour.
1. Square footage X ceiling height = cubic feet of air
example: 2500 square feet X 9 foot ceilings = 22,500 cubic feet of air
2. Cubic feet of air / 60 (minutes per hour) = CFM required for one air change
example: 22,500 cubic feet / 60 = 375
3. Multiply – CFM required for one air change X the number of air changes required = CFM needed
example: 375 X 12 = 4500
Estimating air change per hour:
No smoking = 6-8 air changes per hour
Light Smoking = 10-12 air changes per hour
Moderate Smoking = 12-14 air changes per hour
Heavy smoking = 16+ air changes per hour
In the above example we would need 4500 total CFM to effectively remove the smoke from our 2500 square foot room. In this case we would recommend 4 units that each have about 1100-1200 CFM.
A few things to consider…
If you are using media based smoke eaters remember that as the smoke filters load (become dirty), they restrict airflow. A smoke eater that has 1,000 CFM will only deliver about 600 CFM when the filters are half-way loaded. When sizing media based smoke removal systems, it is best to oversizethem by about 30-40% to make sure that they will still be effective once the smoke filters start to become dirty. Electrostatic smokeeaters do not restrict airflow when they become dirty, but if you add carbon post filters, you should oversize the units by about 10-15% to account for the airflow restriction caused by the extra carbon.
Calculating airchanges per hour is a good indicator of the size of the smoke removal system you will need, or the number of smoke eaters you will need to effectively remove second hand smoke, but it is not the only thing to consider. Remember that a smoke eater relies on airflow and cannot work around corners, through walls or through doorways or archways. In our above example we used a 2500 square foot room and we decided that 4smoke eaters would provide good coverage. If this 2500 square foot areais broken up into several smaller rooms or separated areas, four 1200CFM smoke eaters would not be the best choice. If we are dealing withseveral smaller rooms, it would be best to size each room and choose asmoke eater for each room that can achieve your target air changes perhour.
Number of people/smokers
When designing or sizing a smoke removal system another factor to consider is the maximum number of people and the number of smokers in the area you are expecting. A large smoke eater (1250 CFM) is suitable for about 30 people, with 10 of them being smokers. In our above example where we have calculated air changes per hour in a large room, the four units would be effective if we were expecting a maximum of about 100 peoplewith about 50 of them being smokers. If you expect more people, or more smokers, you should allow for more smoke eaters, more air changes per hour and therefore more CFM and more units.
The above examples and tips should help you determine how many smoke eaters you will need to effectively remove second hand smoke. There are other factors to consider, but if you follow the examples above, you should have an effective smoke removal system.