Operators typically complain of “sudden rushes” of air loud enough to disturb sleep, or of “clicking” and “clacking” sounds associated with temperature regulation cycles. These, however, need not be viewed as normal furnace operation.
Should an old furnace have disturbing noises during temperature regulation cycles, first check that the burners are clean. They may have become corroded over time. The flame rod might need cleaning, and if the flame detector is dirty, it could cause the gas valve to shut down intermittently. This will produce the clicking and clacking sounds associated with the on-off temperature cycling mechanism. It is recommended that the furnace be run in the fall months to test its effectiveness. If the air expelled from the grills is less than 90°F, the furnace might simply require a good clean to prevent unnecessary noise.
When purchasing a new furnace, select one that has a two-stage/variable-speed motor. This technology circumvents any sudden blasts of air or sudden kicking in of the temperature cycling regulator. Instead, it ramps up and down slowly and therefore quietly, even when running in fan-on mode.
Smooth running and vibration-free operation is possible using these technological advancements.
Final note: two-stage/variable-motor furnaces start up in lower-capacity,first-stage mode and for moderate temperature settings. Theycan remain there for most of the time, reaching the temperature setting without moving into the second stage. The result will befuel savings and quieter operation.