A fully designed room can't be comfortable without proper airflow. So how do you appropriately determine the airflow necessary based on the square footage of the space? We've researched how to get the right cubic feet per minute (CFM) for your comfort.
This depends on your home's ceiling height and the frequency of air change per hour (ACH). Supposing your 2,000 square feet has a standard eight-foot ceiling and 2 ACH, you need 533 CFM.
So, how are you going to get the exact CFM? We will discuss the calculation in detail to help you measure it correctly, so keep reading. We'll provide you with other information which may be useful in the future.
How To Calculate CFM?
Here is a step-by-step procedure to assist you in calculating this simple CFM formula.
Get the total area of your room by multiplying its length and its width if the shape is square or rectangular.
- Length x Width = Total Area In Square Feet
For example, the length is 20 feet and 10 feet wide. It will look like this:
- 20 feet (length) x 10 feet (width) = 200 square feet
However, for irregular-shaped rooms like L-shaped, split the room into two squares/rectangles. Separately get their total area then add. The same principle can be used for U-shaped rooms. Look at the example below:
- First half: 10 feet (length) x 10 feet (width) = 100 square feet
- Second half: 5 feet (length) x 5 feet (width)= 25 feet
- 100 square feet (first half) + 25 square feet (second half) = 125 square feet
Measure the height of your ceiling by pinning the end of your tape measure to the floor and stretching it upwards until it reaches the ceiling. Make sure to keep the line straight for accurate measurement.
Ask for assistance if you need to use a step-steel ladder.
Get the volume of a room, which lets you determine the heating and air conditioning needs of a room, with the following formula:
- Total floor area (ft²) x ceiling height (ft) = volume of a room (ft³)
For example, you have a 2,000 square feet area and 8 feet ceiling height. So,
- 2,000 ft² x 8 ft = 16,000 ft³
A 2,000 square feet room has a 16,000 cube feet volume.
Know your room's Air change per hour (ACH). It determines how fast the air inside is being recycled with filtered clean air within 60 minutes. Here are some general air exchange rates per hour for residential and commercial buildings:
- Homes: 0.35-1
- Hotel rooms: 1-2
- Offices, Retail shops: 2-3
- Schools: 5-6
- Sports facilities: 4-8
- Restaurants: 6-8
Multiply the room volume (Step 3) by the ACH (Step 4).
- 16,000 ft³ x 2 (air change frequency in an hour) = 32, 000 ft³
Since CFM has a cube feet (ft³) per minute unit, divide it by 60(minutes). So,
- 32,000 ft³ (per hour) ÷ 60 (minutes) = 533 ft³ per minute
You will need 533 CFM airflow for 2,000 square feet.
Is It Better To Have A Higher CFM?
Higher CFM works best in lower settings where there is a heavy amount of air to ventilate. It is always better to have higher CFM in the kitchen where smoke evaporates when cooking.
What Is A Good CFM For A Floor Fan?
Purchasing a fan that can effectively cool everyone is important. That is why knowing the right fan CFM for your home can be a very good investment. Below is a CFM and floor area estimation to give you an approximation if you do not know the exact room dimension.
- Under 200 square feet: 2,000 to 3,000 CFM
- 200 to 300 square feet (standard bedroom or kitchen): 3,000 to 4,000 CFM
- 300 to 450 square feet (master bedroom or living room): 4,000 to 6,000 CFM
- Above 450 square feet: 5,000 to 9,000 CFM
Note: Areas more than 450 square feet should consider placing multiple fans to keep everyone in the space cool. Aside from the size of the room, three other factors can affect fan CFM:
- Rotation per Minute (RPM): Fan's blade rotation count within 60 seconds. The standard fan runs at 300/350 RPM while high-speed fans are at 380/390 RPM.
- Blade size: The amount of airflow depends on the proportion of the blade. The larger it is, the more powerful it blows.
- Pitch: This is the angle between the propeller blade chord line and the plane of rotation of the propeller. It allows the fan to pick up the air so the greater the blade material, the better the fan can move air.
Read more about fans here: "What Is A Good Airflow For A Ceiling Fan?"
What Is The Average CFM For A Ceiling Fan?
The average ceiling fan CFM ranges from about 4,000 to 5,000 at high speed. It can be seen in its Energy Information Label. Also, when it comes to ceiling fans, the more exaggerated their blade angle is, the higher the airflow.
Read this article to know more about this topic: "What Is A Good Airflow For A Ceiling Fan?"
How Many Blades On A Ceiling Fan Make The Best Airflow?
Ideally, three-blade fans can increase the airflow among the rest of the number-blades. This is because it has fewer blades to drag so it is easier for them to rotate and uses minimal energy to run. However, since the three blades are light, it is the noisiest.
Other higher blade count also provides sufficient airflow and are quieter but moves slower than the three-blade ceiling fan.
What Is The Average CFM For Air conditioners?
Typically, manufacturers recommend using 400 CFM per ton of air conditioning. To determine the best speed to use, measure the total system static external pressure (E.S.P) and look at the blower performance chart.
How Many CFM Do I Need For My Bathroom Exhaust?
In the case of bathroom exhaust, one CFM per square foot of the bathroom area is the case. For example, a 10-foot by 10-foot bathroom needs a 100 CFM fan. If you are planning to buy one, look for the 'HVI-certified' label.
This assures the buyer that the product has gone through rigorous testing.
How Do I Increase The Airflow In My Bathroom?
The bathroom creates a lot of moisture so if you have a weak airflow, it can cause damage to the surfaces. Take note of these tips on how to improve ventilation in your bathroom.
- Put an allowance between the floor and the base of the door.
- Add more insulation to the floor and the walls.
- Use a passive vent by installing a grill in a windowless room.
- Windowless rooms can create airflow by turning on a fan or air conditioner.
What Happens If There Is Not Enough Return Air Vent?
Not enough return air interferes with your HVAC system's proper functioning. Return air maintains the air circulation and lets the air return to the AC system to be cooled or heated.
Do I Need Return Air Vents?
Here are some of the benefits you'll get from having air return vents:
- It maintains air pressure by pulling and pumping the air back into the system.
- Filtering micro particles and debris like allergens, preventing air quality to drop.
- Balance humidity by conditioning the climate indoors.
Preferably, one air return vent per room to maintain good air pressure. But two or three vents can perform better. If you only have one vent throughout the house, it can still manage to do the job but you should open every room door to let the air circulate.
How To Create Airflow In A Room
If your appliance does not have enough CFM to keep everyone from sweating, you can do these tricks to improve the airflow in your room.
- Open the door to allow the hot air which built up inside to flow back out.
- If you don't want your doors unlatched, open the windows instead. It can help draw out the air coming in, allowing your appliance to replace it with new air.
- Open your air conditioner's vent. Setting it to fan mode can help air circulate in the room.
- Create cross-ventilation by placing a fan in front of the open window, facing inward to force the air in. Facing it outward creates a vacuum effect, sucking the hot air inside.
- Add an extra fan in the middle of a huge room to get the air moving.
Read more here: "How To Increase Airflow To One Room."
After knowing all the necessary measurements about effective CFM, decide on the system you will use to meet your place's airflow needs. Don't forget to get a professional's second opinion to make sure you'll choose the best for the greatest comfort. Good luck!