Foul Furnace Odors

Unlike the normal smell of dust burning off when a furnace is turned on for the first time after a long shutdown from summer, putrid odors coming from a furnace often signal something more serious has occurred. A foul odor originating from a furnace often occurs because a dead animal is decomposing inside the furnace. We unfortunately encounter this problem too often, which is usually the direct result of home owners failing to guard their furnace’s intake and exhaust vents properly. Only after these home owners are hit repair bills costing hundreds or even thousands of dollars, do they seek the protection our furnace vent screens offer.

In the image to the right you will see a decomposing animal that was removed from a furnace’s draft inducer motor. Because the exhaust pipe is attached to the draft inducer motor, this animal was trapped inside the draft inducer motor housing where it died a horrible death. The obstruction caused by the decomposing animal also made the furnace inoperable (lockout) until the dead animal was removed and the unit was serviced. A typical service call to remove dead animals from a draft inducer motor can range from as little as $250 to $800, with the higher cost including replacement of the draft inducer motor. Infiltration events from the intake, as noted below, can often be more costly and in some cases require the furnace be replaced.

Burning Smell from Furnace

A burning smell coming from a furnace can be very serious and the unit should be immediately shut down, power to the furnace turned off at the breaker and serviced immediately by a locally licensed HVAC technician. As it pertains to infiltration events, it’s not uncommon for animals to gain entry into a furnace from an unprotected or improperly guarded intake vent. Once inside a furnace, animals often are trapped inside the burner compartment where they may chew on wires which creates an electrical hazard. Encountering dead animals inside a furnace, which have been electrocuted from chewing on wires, is not uncommon. In some cases a live animal, or bees and wasps from a nest within the furnace, may come into contact with the flames and burn. Food, bedding and nests themselves are combustible and may ignite. Please do not underestimate the danger a burning smell from a furnace poses. Though some home owners may be compelled to investigate the burning smell themselves, a partially burned/wounded animal may still be alive inside the furnace. Opening the furnace cabinet can release any trapped animals, bees, wasps, etc. into the dwelling.

Preventing Odors from Infiltration Events

The key to preventing infiltration event related odors, and the costly repair bills that often result from them, is to keep animals and insects outside where they belong. Because the heat produced from a furnace involves combustion, vent screens that guard a furnace’s vents must maintain a high rate of airflow (especially in winter). Because of this, we manufacture 70% airflow rated insect screens for use in the warmer months when insects are active and 90% airflow rated vent screens for use in sub-freezing temperatures and throughout winter. Our best practices page describes how to use our vent screens properly to guard against all seasonal threats.