Direct answer: If mice chewed a range hood duct, the usual fix is replacing the damaged section of range hood ducting and sealing the entry point at the exterior vent cap or wall opening. Do not run the hood until you know the duct is still intact and no wiring or greasy nesting material is involved.
Most likely: Most often, mice get in through a loose or damaged exterior vent cap, then chew thin foil or flex duct near the hood or wall cavity.
Start by separating three lookalikes: torn duct only, blocked duct from nesting, or chewed wiring near the hood. Reality check: if mice were in the vent path, there is usually more than one damaged spot. Common wrong move: patching a greasy torn duct with ordinary tape and calling it done.
Don’t start with: Do not start by stuffing the vent with mesh, tape, or foam from inside the duct. That can cut airflow, trap grease, and make the hood less safe.
The hood fan runs, but you feel air leaking above the hood, inside an upper cabinet, or around the duct chase.
Start here: Check the visible duct connection above the hood for a torn, crushed, or disconnected section before assuming the fan is bad.
Steam and cooking smoke linger longer than usual, and the outside vent flap barely moves.
Start here: Look for nesting or chewed duct collapse in the shortest accessible section between the hood and the wall or ceiling.
You smell stale grease, mouse odor, or a dirty attic-wall smell when the fan turns on.
Start here: Inspect for droppings, nesting, and grease-soaked contamination around the hood top, duct opening, and exterior vent cap.
The fan cuts out, lights flicker, or you see chewed insulation near the hood wiring compartment.
Start here: Stop immediately and treat this as possible electrical damage, not a simple duct repair.
Thin foil or light flex duct is easy for mice to damage, especially near warm greasy areas or where the duct rubs a sharp edge.
Quick check: With power off, remove the hood filter and look upward with a flashlight, then inspect any accessible duct above the hood for holes, tears, or loose joints.
A stuck-open flap, broken screen, or loose cap gives mice the easiest entry point into the vent run.
Quick check: From outside, check whether the vent flap closes fully and whether the cap is cracked, loose, or missing pieces.
Mice often drag insulation, paper, and food scraps into the duct, which cuts airflow even if the duct is not fully torn open.
Quick check: Run the hood briefly only if there is no sign of wiring damage, then see whether the exterior flap opens strongly or barely moves.
If mice stayed near the hood body, they may chew wire insulation or leave droppings and urine around the fan housing.
Quick check: Turn power off and inspect the hood wiring compartment and fan area for chewed insulation, scorch marks, droppings, or nesting.
Mouse damage around a greasy exhaust path can involve sharp metal, contamination, and sometimes wiring. You want to rule out the dangerous version first.
Next move: You have a safer starting point and know whether you are dealing with simple duct damage or a higher-risk contamination or wiring problem. If you cannot safely access the hood area or the damage is inside a finished wall or ceiling, stop and arrange vent or pest repair help.
What to conclude: Visible droppings and nesting point to contamination cleanup along with repair. Any sign of electrical damage moves this out of basic DIY.
Most mouse entry and chewing damage shows up at the two ends of the run, not magically in the middle first.
Next move: If you find a torn duct end or a bad vent cap, you have a likely repair path without opening more of the house. If both ends look intact but airflow is still poor or odor is strong, suspect a hidden nest or damage farther along the duct run.
What to conclude: Damage at the hood end usually causes indoor air leakage. Damage at the vent cap usually explains how the mice got in.
A split duct and a plugged duct can both cause weak exhaust, but the repair is different. One leaks air; the other chokes airflow.
Next move: You can now aim the repair: replace damaged duct sections, or open the run for proper nest removal and cleanup. If airflow is poor and you cannot locate the blockage without opening finished surfaces, this is a good place to bring in a vent contractor or pest-remediation pro.
Once the bad section is visible, the clean repair is usually straightforward: replace the damaged range hood duct section and fix the entry point so it does not happen again.
Next move: The duct path is intact again, the entry point is corrected, and the hood can move air outside instead of into the house. If the hood still leaks, smells, or has weak airflow after the visible duct and cap are repaired, there is likely hidden damage, deeper contamination, or internal hood damage.
You want normal exhaust airflow and a closed vent path when the hood is off. The goal is to keep mice out without choking the vent.
A good result: You have a working exhaust path again and a better chance of keeping mice from re-entering.
If not: If airflow is still weak or odor remains after confirmed repairs, stop chasing it with more tape and get the concealed run inspected.
What to conclude: A good repair gives you strong outdoor discharge, no indoor leakage, and a vent flap that closes properly at rest.
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Only as a very short-term hold, and not on a greasy, badly torn, or crushed section. If mice chewed through the duct, replacement is usually the proper repair because tape on dirty ducting does not last well and does not fix hidden damage.
Not until you know the duct is intact and there is no nest, heavy contamination, or chewed wiring. If the hood smells bad, leaks air indoors, or acts electrically strange, leave it off until it is inspected and repaired.
Most often through an exterior vent cap with a flap that sticks open, a broken cap, or gaps around the wall penetration. Once inside, they tend to damage the easiest thin duct section near the hood or wall opening.
Then suspect a hidden blockage, crushed duct, or damage farther along the run. If you cannot see the bad section without opening finished surfaces, it is time for vent service rather than more guessing.
If this was a one-time entry and you found a clear damaged duct or bad vent cap, repair may be enough. If you see fresh droppings, repeated activity, nesting, or multiple entry points, handle the rodent problem too or the vent damage will come back.