What can be an indication of a clogged return air duct in a heating system?

An indication of a clogged return air duct in a heating system is often seen through uneven heating throughout the property. When a return air duct is obstructed or clogged, it hampers the circulation of air, preventing the heating system from effectively distributing warm air to all areas of the home. This can result in some rooms being warm while others remain cold, highlighting that the air is not flowing properly due to the blockage.

The other options may suggest issues with a heating system but are not as directly tied to the specific problem of a clogged return air duct. For instance, a cool draft from vents might imply other issues with the heating system or insulation, while an increase in energy bills and persistent odors could point to various problems that do not specifically relate to the condition of the return air duct. Therefore, uneven heating is the most direct indicator of a clogged return air duct.