This troubleshooting problem brings you to a three-bedroom, ranch style home on a concrete slab, which, as most typically do in the particular area of the Southwest in which this home is located, employs a rooftop evaporative cooling system in the summer and an upflow forced-air gas furnace for heating in the winter. The furnace, according to the customer, isn’t heating enough because one of the bedrooms “just won’t get comfortable.” Other technicians have been there before you to check on this problem over the past three years, but the problem persists. When you arrive, you find that this air handling system employs an extended plenum with supply registers in the ceiling as shown in Figure 1.
You also note in your overall survey of this home that the return duct system is under the slab, and each room has its own return air grille. The last bedroom on the supply duct system is served by the branch shown at the bottom right of our illustration, and the customer explanation of the situation is that the system has never performed properly. You also note that some of the registers in the system have been adjusted almost totally closed in an effort to supply adequate airflow to the problem bedroom.