Is it true that rodents cause 20-25% of house fires?

No — that figure is not supported by any primary NFPA or U.S. Fire Administration data. It traces back to an October 2012 pest-industry trade-magazine article that presented the number as 'estimated' without citing any actual data source, and it has been repeated in marketing copy ever since without a real basis. Neither NFPA nor the U.S. Fire Administration publishes any rodent or animal share of house fires, and national fire incident data has no standalone category attributing fires to animals. This invented percentage should never be repeated as fact — what's real is the underlying mechanism, described next.

If the percentage is invented, is the fire risk from rodents in HVAC systems real at all?

The mechanism is real, even though the specific percentage isn't. Rodents that nest inside ductwork or near air handlers can chew wire insulation, and U.S. Fire Administration data on residential electrical fires shows that short-circuit arcing from defective or worn insulation is a documented ignition pathway, within a broader category where electrical failure or malfunction is the leading factor overall. Damaged insulation from rodent gnawing fits squarely into that pathway. So the correction runs in both directions: don't repeat the invented 20-25% figure, but don't dismiss the gnawing-to-arcing mechanism either — it's a genuine, if uncommon, escalation.

What does rodent damage inside an HVAC system typically look like before it becomes a safety issue?

Most rodent-related HVAC damage shows up first as efficiency and contamination problems rather than a safety event: chewed duct insulation reducing heating efficiency, air leaks at gnawed duct seams, and droppings or urine getting circulated through the house every time the blower runs. Wiring damage is a smaller subset of cases, typically found when a technician opens an air handler or duct run for another reason and notices gnaw marks on wire insulation. That's the point at which a licensed electrician should assess the wiring specifically, rather than treating it as routine duct repair.

How do I know if my HVAC system already has a rodent problem?

Reduced heating efficiency without an obvious mechanical cause, an unusual odor when the system runs, visible droppings near vents or in an accessible duct run, or scratching sounds that seem to come from inside ductwork are all reasonable signals to have the system inspected. Because this issue straddles pest control and HVAC service, the most efficient path is usually a pest professional to confirm rodent activity and begin exclusion, paired with an HVAC technician to inspect ducts, insulation, and wiring for damage that needs repair rather than just pest removal.

Daniel Brady · NH-Licensed Pesticide Applicator · License #782664

Do Pests Infest HVAC Systems?

Heat draws them in

Rodents are genuinely drawn to the stable warmth, shelter, and insulation inside HVAC ductwork, air handlers, and the chases around them — and once they're in, they can damage the system by chewing insulation and, in some cases, wiring.

Worth fixing for efficiency loss, contamination, and repair cost. It rises to a genuine safety concern only where gnawing exposes energized wiring, which is real but not common — and it is not the fire hazard the pest industry has claimed.

At a glance

The mechanism: Heat draws them in
Who fixes it: A licensed pest pro
The rest lives at: Can rats cause electrical fires?

Cause, or just reveal?

Heat draws them in

What's really happening

Heat doesn't spawn pests — it changes what you notice

The season and the building set the stage before the thermostat ever comes on. Here's the honest chain of events, spelled out.

What's really happening

A rodent enters through an exterior penetration, finds the warm, quiet, insulated spaces inside HVAC ductwork and equipment, and nests in or around ducts and cabinets, chewing insulation and sometimes wiring. The consequences are reduced efficiency, air leaks, and contaminated ducts as droppings and urine circulate through the blower — and where wire insulation is damaged, a genuine arcing ignition pathway. U.S. Fire Administration data on residential electrical fires found that electrical failure or malfunction was the leading ignition factor by far, and that short-circuit arcing from defective or worn insulation accounted for a meaningful share of those fires. Damaged wire insulation is precisely the physical pathway rodent gnawing can create.

Source:U.S. Fire Administration— "Residential Building Electrical Fires (2014-2016)," Topical Fire Report Series Vol. 19 Issue 8 — electrical failure/malfunction as leading ignition factor; short-circuit arc from worn insulation

The honest router

Is this an HVAC problem or a pest problem?

Who actually fixes it

A licensed pest pro

Removing and excluding the rodents is the primary fix, and this page genuinely straddles two trades — a pest professional handles the animal, while an HVAC technician assesses and repairs ducts, insulation, and cabinets.

Escalate when

Damaged wiring is found — a licensed electrician needs to assess and repair any exposed or energized wire, since that's outside both pest control and general HVAC scope.

Who owns the rest

This hub owns the heating-system angle

General winter behavior, rodent control, and equipment-damage severity live in siblings that already earn them. Here's exactly where.

This page owns why HVAC systems get infested and what the heating-system stakes are. Damage severity, including the full fire-myth correction, belongs to our pest damage and risks hub; rodent exclusion belongs to our mice & rats FAQ.

Can rats cause electrical fires?

Can rats chew through walls or floors?

Local to New Hampshire

How this calibrates for NH

New Hampshire context

New Hampshire homes with ducted forced-air heating and attic or crawlspace duct runs give rodents warm, protected corridors during a months-long heating season, and because the equipment runs so much during that season, any contamination present gets circulated widely once rodents are established in the system.

NH-licensed applicator #782664 (NHDAMF, RSA 430) · NEPMA member · family-owned since 2017.

Follow-up questions

Frequently asked

Sources(2)

[1]
U.S. Fire Administration
"Residential Building Electrical Fires (2014-2016)," Topical Fire Report Series Vol. 19 Issue 8 — ignition factors including short-circuit arc from worn insulation
[2]
NFPA
"Home Fires Caused by Electrical Distribution and Lighting Equipment" — no rodent/animal fire percentage exists in NFPA data

Written & reviewed by

Verified

Daniel Brady

NH-Licensed Pesticide Applicator · License #782664 (NHDAMF, RSA 430)

Daniel Brady is the New Hampshire–licensed applicator behind Anchor Pest Services, a family-owned pest control company serving the Manchester area since 2017.

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