HVAC ducts per room

Is there a rule of thumb (or code) which provides an indication of number of HVAC ducts which should be present per habitable room? Perhaps a calculation for number of ducts per room square footage? I as in a newly built home in which the living room was approx. 30x15 with vaulted ceilings and had one duct in it. I had the opportunity to look in the ‘feature home’ for this sub which happened to have the same floor plan and it had 3 ducts in the same room. Seemed like the builder was trying a bit of bait and switch?? In the same house, there was no duct in a habitable 1/2 bath. Again, in the ‘feature home’ the duct was in this 1/2 bath.

Thanks for any info,

At least one supply register in each room. Any more than that is dependent on the builder if he wants better air flow through the room.

The “code” I believe would be in Manual D which covers the duct and airflow side of the HVAC spectrum. I don’t believe a rule of thumb would be of much use. Too many variables come into play in determining what is appropriate for duct sizing, vent placement, vent quantity and size, etc. What if there was only 1 big honkin’ vent? What if there were 3 or 4 really small ones? Which case would be more appropriate?

The extra vents might be part of the upgrade package.