Maintaining and Upgrading Existing Duct Systems Regardless of where they are installed, ducts should be well sealed. Aside from sealing your ducts, the simplest and most effective means of maintaining your air distribution system is to assure that furniture and other objects are not blocking the air flow through your registers, and to vacuum the registers to remove any dust buildup. Existing duct systems often suffer from design deficiencies in the return air system, and modifications by the homeowner (or just a tendency to keep doors closed) may contribute to these problems. Any rooms with a lack of sufficient return air flow may benefit from relatively simple upgrades, such as the installation of new return-air grilles, undercutting doors for return air, or installing a jumper duct. Some rooms may also be hard to heat and cool because of inadequate number of, or size of supply ducts or grilles. If this is the case, you should first examine whether the problem is the room itself: fix any problems with insulation, air leakage, or inefficient windows first. If the problem persists, you may be able to increase the size of the supply duct or add an additional duct to provide the needed airflow to the room.