An air conditioner with wires attached to it.

Dangers of Animals and your HVAC System

Do you have four, six, or eight-legged roommates?

No, not your pets. These critters aren’t so friendly.

Have you ever heard something scurrying in your attic? Or seen something crawling in your unit?

Don’t panic, but your “roommate” might be damaging your unit.

What Types of Pests Can Invade Your HVAC System?

Bugs (Ants & Spiders)

How can something so small cause so much damage?

Whether it’s an ant infestation chewing on your electrical components or a spider building webs over sensors, these nasty critters can cause a bunch of problems.

Squirrels & Racoons

While they may look cute and cuddly, squirrels and racoons wreak havoc on HVAC units! They have sharp claws and teeth, and they often get trapped in places they don’t belong.


You don’t need hands or feet to damage a unit. Snakes will still find their way into your unit, and they can damage your electrical components in the process.


Have you ever tasted wiring? We don’t recommend it. For some reason, rats and mice think it’s a gourmet meal! They’ll gnaw their way right though anything, leaving you with a damaged unit.

What Types of Pests Can Invade Your HVAC System?

You may see it as a part of your heating system, but birds and squirrels see it as a good spot for nesting.

Blocked Flue

Unfortunately, birds and squirrels don’t always pick the best places to build their nests. Sometimes, they build in the flue pipe of your heating system. Your flue pipe’s job is to direct deadly gases, such as carbon monoxide, out of your home. If the flue is blocked, the gas can’t get out. It comes back into your home and the air your family breathes.

Everyone knows birds build nests, but did you know squirrels do, too?

Chewed Wires & Damaged Electrical Components

Wires, safeties, flame sensors… oh my! All of these (and more) look rather tasty to animals like rats and squirrels. Unfortunately, when they chew through wires and other components, it can cause electrical problems in your unit.

It’s also not uncommon to find snakes caught in HVAC units. Your system gets warm, and snakes love warmth! They’ll try to slither their way in and around electrical components, but they often end up electrocuted in the process.

Even ants can be a menace when it comes to electrical equipment! Sometimes, ants will chew on your wiring or even carry dirt into your unit.

When critters chew on things in your unit, it can expose wires, leaving your system and home vulnerable to further damage.

mouse that died chewing wires in an hvac unit
Not only might there be webs in your furnace, but sometimes birds will find their way in and get stuck.

Spider Webs Inside Furnace

Nobody likes to think about spiders in their house.

Even if you don’t see spiders in your home, they’re still bad for your furnace. Your furnace has several types of safety sensors that tell the unit when something has gone wrong. If spiderwebs build-up, the sensors will detect them and eventually shut down your unit because it senses something unusual inside it. Cobwebs, (abandoned and dusty spider webs) can also pose a tricky problem because, as dust collects, they grow bigger and block sensors even more.

Recommended: “5 Furnace Safety Features You Should Meet”

Holes in Ductwork

What if you found yourself somewhere strange with no clue how to get out.

Scary, right?

Sometimes, opossums and stray cats find their way into ductwork. When this happens, they might claw or chew through it while trying to escape. Rats and mice cause issues with your ductwork too! They enjoy the insulation itself, and sometimes they chew holes through it. Your ductwork is essential to delivering and removing air throughout your home, so when animals claw through it, that could spell trouble for your HVAC unit.

Rats, cats, opossums, and other critters sometimes find their way into your ductwork and chew on it or scratch it. This can cause a huge mess!

Prevent the Dangers of Animals in Your Unit and Ductwork with Regular Maintenance

There’s no foolproof way to prevent animals from messing with your HVAC system, but with regular maintenance, you’re much more likely to catch these furry (or scaly) visitors before more damage can be done!

Morris-Jenkins offers one-time and routine HVAC maintenance to help your family before these critters cause damage to your unit and your wallet. Want to ensure the best protection? Become a Priority Advantage® Member and we’ll check your systems twice a year!

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