Enlarging duct size vs adding air vents

[Hai G.]

Hi BP,

My rental unit (2bd 1100 sq ft) only has 3 total air vents for the HVAC system. This results in the house heating up very slowly. I’m looking to change this.

A heating guy said it’s better to enlarge the ductwork (currently 6”, suggested to make it 10”) than to add air vents to increase airflow. I was wondering if it’s better to add more supply vents as the airflow seems fine from the existing vents, but there are just too few of them (and spaced too sparsely in the house).

Any thoughts from the community?

Thanks, 

Hai