In a house with a heat pump, is it OK to close off vents in some rooms?
It's generally not a good idea to close off vents in the distribution system, because
reducing airflow raises the condensing pressure in the inside coil—which affects system
performance. The effect depends on the original system design and how it was balanced.
An alternative would be to rebalance the ductwork system, directing
the design airflow through main living areas of the house and reducing airflow to
perimeter rooms. If total design airflow is maintained over the coils, the unit condensing
pressure should not increase and heat pump performance would remain about the same. If
your client is interested in pursuing such a measure, he could contact a HVAC design
engineer to review the duct sizes and airflows in the house to see if it can be rebalanced
without restricting airflow over the condensing coil (inside coil).