Can Mice Get Into My Ductwork?

Yes. Mice can absolutely get into your ductwork — especially in homes with basements, crawlspaces, or older duct systems.

How They Get In

These are the most common entry points:

• Damaged return air ducts — tears, loose joints, or disconnected ducts in the basement or crawlspace are one of the biggest entry points.
• Around the furnace or air handler — small gaps where ducts connect can be large enough for a mouse.
• Wall cavities — mice travel inside walls and enter through openings where ductwork passes through framing.
• Floor registers — occasionally they climb up through floor vents if they’ve already entered the duct system elsewhere.
• Exterior penetrations — openings where pipes, wiring, or utilities enter the home let mice inside, and from there they find the ductwork.

Signs You May Have Mice In Your Ducts

• Scratching or scurrying sounds, especially at night.
• A musty or urine-like odour when the furnace starts.
• Droppings near floor registers or around the furnace.
• Nesting materials (insulation, paper, fabric) inside ducts.
• Reduced airflow if a nest partially blocks a duct.

Is It Dangerous?

Yes. Mice in your ductwork can:

• Contaminate your ductwork with droppings and urine.
• Introduce bacteria and allergens that circulate throughout the home.
• Build nests that restrict airflow.
• Damage flexible ductwork by chewing through it.

What Should You Do?

1. Find and seal the entry point.
2. Remove the mice using traps — avoid relying solely on poison inside the home.
3. Have the contaminated ductwork cleaned if there’s evidence of nesting or droppings.
4. Repair or replace any damaged ducts to prevent future infestations.