Are Pests Living Inside My Home’s Ductwork?

By Horizon Pest Control

Unlike the rigid, metal ductwork that you see action stars crawling through in Hollywood blockbusters, most residential HVAC air ducts would not support the size or weight of the average human adult. Pests like rodents and cockroaches, however, are a different story.

Below, we’ll explain:

  • How pests get inside air ducts
  • Signs that pests are inside your ductwork
  • Health risks associated with pests in air ducts


Typically, pests get into your ductwork by crawling through tiny rips, unsealed gaps, and vents, and they have no trouble traveling along your cramped air ducts from one space to the next.

Mice and rats can even chew holes into your ductwork with their sharp incisors. Just how strong are their teeth? To give you an idea, rats’ teeth rate harder on the Mohs hardness scale than even copper and iron. This allows them to chew through a variety of durable materials, including:

  • Glass
  • Plastic
  • Wood
  • Brick
  • Aluminum sheeting

When you consider that most ductwork is made of fiberboard, sheet metal, fiberglass, or steel springs covered in thick plastic, it’s no wonder that rodents can easily chew their way inside.


Now that you understand how cockroaches, rodents, and other pests can enter air ducts, you need to know what “red flags” mean you have an infestation in your ductwork.


Sometimes the evidence of an infestation is visible in the form of what the pests leave behind. Mice droppings and rat droppings look relatively similar, like brown or black grains of rice. The major difference is that rat droppings will simply be bigger than those of mice. Cockroach droppings look more like black pepper or coffee grounds.

Bad Smells

Considering pests don’t bother to use the toilet, you’re bound to smell them once they start invading. A stale, ammonia-like odor coming from your air vents is a major indicator that rodent urine is present. You might also notice your cat or dog paying particular attention to a certain vent or getting into “hunter” mode around it. If you see this behavior, it’s time to grab a flashlight and investigate the air duct because your pet is probably smelling a rodent.

Cockroach droppings also emit a foul odor caused by pheromones. This pungent scent is often described as damp, musty, oily, and generally unpleasant.

Smudge Marks, Stains, and Tracks

Although it might be nightmare-inducing, shining a blacklight over your air duct walls can reveal numerous signs of pest activity. Along with footprints, rodents leave behind urine stains and smudges. Cockroaches leave behind dark, irregular streaks that you can use a flashlight to see.

Scratching Sounds

Sometimes you can hear pests moving around in your ductwork. Mice, rats, and cockroaches are most active between dusk and dawn, so you’re most likely to hear them scratching and skittering around during this time frame.

Rips and Gnaw Marks

As mentioned above, pests can chew their way through ductwork. If you take a flashlight into your attic or crawlspace (where the majority of the air ducts are typically located), you might see the places where rodents have ripped or chewed the ductwork material.

Skins and Eggs

Though rodent dander can be hard to differentiate between dust just by looking at it, you can spot cockroach skins and egg capsules with the naked eye. Shedded cockroach skins are brown and have a cockroach shape. Their egg capsules look like little tan, brown, or black pills.


While you don’t want a pest infestation in any part of your home, there are some specific health concerns that come with pest activity in your air ducts. Keep in mind that your central heating and air conditioning system circulates your indoor air continuously throughout your home, which means that whatever is lingering in your air ducts can get circulated too.

An Increase in Allergic Symptoms

Humans can experience allergic reactions to things like rodent dander, saliva, urine, and droppings, as well as the saliva, waste, skins, and bodies of cockroaches. If you find that your “seasonal” allergies aren’t going away when expected, your symptoms could be due to pest allergens circulating throughout your indoor air.

An Increased Risk of Asthma Attacks

Rodents and cockroaches are well-established asthma triggers. Researchers are also exploring evidence about the link between cockroach allergens and the development of asthma in preschool-aged children.

An Increased Risk of Contracting Hantavirus Disease

Hantaviruses are spread mainly through rodents. Hantavirus-carrying rodents in the U.S. include the cotton rat, deer mouse, rice rat, and white-footed mouse. Hantavirus transmission can occur multiple ways but the most common way it’s transmitted to humans is through airborne transmission: a human inhaling air contaminated by an infected rodent’s waste or saliva.

The airborne transmission of hantaviruses is particularly concerning when you think about mice and rats traveling through your air ducts–and what they leave behind in your ductwork. If rodents start contaminating the air in one part of your home, your HVAC system can circulate that air throughout the rest of your living space.

Since 1970, Horizon Pest Control has been working to eliminate pests from New Jersey & New York homes. Contact us today to schedule your pest control service: (201) 447-2530.

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