So, in our example, you judge the customer’s window to require 5% more room airflow. If the window was 6 feet x 15 feet, it most likely would require a 30% increase in room airflow.

Room airflow of 5% or 7 cfm was added for this window, where 42 cfm would be added for a very large window.

You and your customer make the call while looking at the window. You’ll be surprised how easily most customers assess the percent to add or subtract when estimating room airflow. The decision is quite natural.

Remember, if the estimate is 5% or 10%, the difference between the two estimates is only 7 cfm in the room. Don’t overcomplicate the process. Make participation fun for your customers.

You’ll be surprised how easily most customers assess the percent to add or subtract when estimating room airflow. The decision is quite natural.

— Rob “Doc” Falke

Add together the percentages to include in the base room airflow. In the report, you’ll see 30% is added to this room’s estimated airflow.

Step Five. Subtract Room Airflow. Some factors require we subtract a percentage, within the percent ranges shown, to deduct airflow for each room feature that will decrease required room airflow. The customer’s room has a large tree shading one outside wall from the summer heat. We reduce airflow by 10% because the tree decreases the room’s heat gain.

Add together the percentages to be deducted from base room airflow. 10% of room airflow is deducted in this example.

Step Six. Estimate Room Airflow by taking the base room airflow calculated in Step Three, then add or subtract the other factors based on your estimates.

Multiply 141 cfm of base room airflow times 30% to add 42 cfm. Multiply the base room airflow times 10% to deduct 14 cfm from the base room airflow.

The estimated room airflow is 169 cfm. Round up to the nearest 0 or 5 cfm to find the customer’s room needs 170 cfm.

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