The heat smells when you first turn it on primarily because dust and debris have settled on the heating components during the time the system was off. When you turn the heat on, this dust burns off, producing a distinct burning or dusty smell. This is completely normal and the odor usually goes away after a short time once the dust has been burned off. Other possible causes of smells when first turning on the heat include:
- A musty or mildew smell, which indicates mold or bacteria buildup in the heating coils or ducts, especially common in heat pumps.
- A sulfur or rotten egg smell, which is a serious sign of a gas leak in gas furnaces and requires immediate attention.
- An electrical burning or fishy smell, which may indicate overheating or an electrical fault.
Generally, the first-time burning dust smell is harmless and disappears after use. If the smell persists for more than a day, worsens, or if you notice unusual odors like rotten eggs or fishy smells, it is important to turn off the system and contact an HVAC professional for inspection and repair.