One question I often hear from HVAC professionals is "Doc, if there was just one thing I could do for each system to improve performance the most, what would it be?" Let's take a look at the answer to that question as it pertains to your specific role in this industry.
For installers, seeking just one thing you could do for every system you install, the answer would be: Assure each return duct installed in an unconditioned space is completely sealed and that the proper duct insulation has no gaps.
Return duct leaks from ducts located in areas surrounded by hot or cold air such as attics pose the greatest threats to a system’s efficiency that usually goes undetected for the life of a system. A 300 CFM leak through a return duct in a hot attic can easily pull in enough heat to reduce cooling system capacity a ton or more.
To verify the job is done right, when the system is started up, measure the air temperature entering the return grille farthest from the equipment and subtract from the air temperature entering the equipment. The difference should be less than 10% of the temperature change over the equipment.
For maintenance techs, seeking just one thing you could do for every system you maintain, the answer would be: Ask each customer which of their rooms is the least comfortable. Then spend 5 minutes searching for an obvious solution to their problem.
Go beyond your normal checklist and make a change for good that your customers will appreciate for years to come. Adjust louvers on a supply register; open a damper that was installed in the closed position 10 years ago. Connect a broken duct in an attic or discover the insulation that was never installed above the master bedroom. Your customers will love you and remain loyal for life.