How to Calculate Ducting Sizes

When you are designing or upgrading rooms in your house, such as a kitchen or bathroom, it is important to install a proper ventilation system. To have a properly installed ventilation system, you need to have the right duct size. Luckily, there is a fairly easy way to go about calculating the needed duct size for a simple bathroom or the entire house.

Instructions

1. Pull out the blueprints or square footage of the room in which you plan to add a ventilation system. You need to know exactly how many square feet the room is to calculate the ducting size.

2. If you do not know the how many square feet there are, measure the width and length of the room. Multiply the two numbers together, and this is its square footage.

3. Multiply the number of square feet by .75 for any room that is not a kitchen or bathroom. The number you come up with is the CFM, or cubit feet per minute, airflow. This is how much of ducting you need for the room.

4. Multiply the square footage of the kitchen by 2 to come up with its CFM. The kitchen requires the most CFM of all the rooms in the house.

5. Ignore the square footage calculation for the CFM of a bathroom. If you have a bathroom of 64 square feet, 64 is the CFM of the room.

References

• Panasonic.com: Central ventilation size
• Correct sizing of residential air-conditioning