manual J is a method of determining a structures heat loss and gain. manual D is a method of determining the total equivalent length of a duct system to determine what friction rate loss to use on a duculator.
Both are critical to properly sizing, designing and installing a complete HVAC system. Anything short, is just varying degrees of guesswork or a matter of simply throwing it together.
IF the transmission died in your car, would you want them to use a mfg specific service manual and procedures, or just throw it together because they are "all about the same".
A couple of books from the bible of the HVAC world.
Though you'll still need to run a Manual D so you know the system is going to work properly. Far too many never check airflow at all...
thnx guys,..this site is helpin me lot...a couple of mnths earlier i was nt even knowin d HVAC full form, somebudy askd me n i told him it mayb high voltage alternating current:grin2:..hehe...bt now m learning day by day n also implementing it my project