In order to ensure proper ductwork sizes for air conditioning and heating ductwork, HVAC professionals will use a duct calculator, or " ductulator," to perform duct calculations.And now, thanks to the modern advances of the internet, one can find a free ductulator online. The basic ductulator for sizing of residential air duct systems will require inputs for the friction rate, the type of supply
. and return ductwork used (PVC or aluminum, sheet metal, fiber board or flexible) and the airflow in cubic feet per minute (CFM) for both the supply and return ducts.After entering that information, the free online ductulator calculates the duct size and provides information for both round and rectangular ducts, listing the smallest duct size for the inputs that is allowable within maximum velocities listed in the ACCA manual D.The results for round ductwork include the calculated exact duct diameter, the diameter adjusted for velocity and the rounded diameter (the actual duct size that should be used - the diameter for round ductwork is rounded up to the nearest inch, unless it is within two percent of the smaller diameter, where it will be listed as that smaller diameter).All three diameter listings for round ductwork (exact, adjusted and rounded) are listed with the corresponding airflow in feet per minute for each. The ductulator will also display any messages relevant to the data entered, such as recommending that in the case of non-standard duct sizes either the diameter be increased by 1", the airflow should be split into two or more ducts, or a rectangular duct should be used.Results for rectangular ductwork calculations are presented next to the drop-down listing where the length of duct side A was entered. The ductulator calculates the size needed for side B and lists the airflow for each in feet per minute. Calculations for rectangular ductwork are rounded up to the nearest 1/4 inch.The free ductulator also includes a velocity calculator, where airflow velocity in feet per minute (FPM) can be calculated for round ductwork by entering the diameter of the duct and the CFM rate, or for rectangular ductwork by entering the measurements of both sides (to calculate the area) and the CFM rate.The online duct calculators are not only free to use, but very helpful in planning dimensions for correctly sized ducting. More reference links: http://efficientcomfort.net/jsp/ResDuct_Web.jsp http://efficientcomfort.net/jsp/DuctCalculator_Web.jsp
