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

No — that figure is invented pest-industry marketing copy, traced to a 2012 trade-magazine article with no cited data, and it does not appear in any NFPA, USFA, or NFIRS fire-statistics report. NFPA allocates unknown-cause fire data proportionally rather than leaving a large unexplained pool for rodents to occupy, and NFIRS has only a generic 'Animal' ignition-factor code with no rodent-specific category or published percentage. Even the London Fire Brigade, responding to a Freedom of Information request, confirmed it holds no data category from which such a percentage could be derived. The gnawing-causes-arcing mechanism behind the myth is real; the 20-25% figure attached to it is not.

If the fire statistic is false, is rodent wire-chewing actually dangerous?

The mechanism is real even though the prevalence statistic is not. Rodent incisors grow continuously, so gnawing is compulsive, and wiring insulation is a common target. If a rodent strips insulation off an energized conductor, NFPA documents that the resulting arc fault 'can produce enough heat to ignite a fire' — that part is genuinely sourced. What's not supported is the claim that this happens in a fixed, large percentage of house fires nationally. The honest takeaway is: treat visible gnaw marks on wiring as worth inspecting promptly, without assuming your specific house is now a statistical fire risk.

How can I tell if rodents have chewed wiring near my heating system?

Look for gnaw marks on visible wiring, duct insulation, or baseboards near the furnace, boiler, or equipment cabinet, along with flickering lights, unexplained breaker trips, or intermittent no-heat problems, any of which can indicate chewed control or energized wiring. Dark, pointed droppings near the equipment and shredded insulation debris are additional signs a rodent has been active in that area. Because most of this wiring runs inside walls or equipment housings, an HVAC technician or electrician may need to open the unit to confirm the extent of any damage rather than relying on what's visible from outside.

What should I do if I find chewed wiring near my furnace or boiler?

Treat visible chew marks on wiring as a call to action, not something to monitor. Have a licensed electrician inspect and repair any damaged conductors, especially if the wiring is energized, and bring in a pest professional to confirm what animal is responsible and exclude it from re-entering — Anchor offers a free quote for that inspection. Avoid touching or attempting to repair energized wiring yourself, and if you notice a burning smell, scorching, or repeated breaker trips in addition to chew marks, treat that combination as urgent and call an electrician right away rather than waiting.

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

Can Pests Chew Heating Wires and Insulation?

Damages the system

Yes — rodents genuinely chew wire insulation and pipe/duct insulation, a real and well-documented behavior with a real, if rare, ignition pathway if the wire is energized.

This is worth fixing and worth inspecting, not a house that's statistically likely to burn down. The commonly repeated '20-25% of house fires' figure has no basis in NFPA or USFA data — see below — but the arc-fault mechanism it distorts is genuinely documented.

At a glance

The mechanism: Damages the system
Who fixes it: A licensed pest pro
The rest lives at: Can rats cause electrical fires? Mechanism vs. the myth

Cause, or just reveal?

Damages the system

Yes — rodents genuinely chew wire insulation and pipe/duct insulation, a real and well-documented behavior with a real, if rare, ignition pathway if the wire is energized.

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's incisors grow continuously and must be worn down by gnawing. Wire insulation — plastic or rubber, sometimes plant-based — offers ideal resistance for that purpose, so gnawing strips it away. If the exposed conductor underneath is energized, it can arc, and NFPA documents that an arc fault "can produce enough heat to ignite a fire." That mechanism is real; the widely-quoted prevalence statistic built on top of it is not.

Source:NFPA— Non-Home Electrical Fires report (Campbell, 2019) — arc-fault definition and ignition mechanism

The honest router

Is this an HVAC problem or a pest problem?

Who actually fixes it

A licensed pest pro

Eliminating and excluding the rodents stops new gnawing; a licensed electrician then repairs any wiring damage already done, since inspecting and re-terminating energized conductors is licensed electrical work, not pest control.

Escalate when

Visible chew marks on energized wiring, flickering lights, or repeated breaker trips — call an electrician immediately rather than waiting for a routine inspection.

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 hub owns the heating-wiring/insulation angle and the fire-statistic correction as it relates to the heating system. The full damage-and-risk severity ledger, including the complete myth-vs-mechanism breakdown, lives on our pest damage & risks FAQ; rodent control is owned by our mice & rats FAQ.

Can rats cause electrical fires? Mechanism vs. the myth

Can pests cause short circuits or fires?

What steps prevent mice from entering a home?

Local to New Hampshire

How this calibrates for NH

New Hampshire context

New Hampshire's months-long heating season keeps furnace and boiler wiring energized and warm for most of the year, and field mice are documented to shift undercover in winter and favor spots near warm electrical components — so gnawing damage near heating equipment is a cold-season pattern here, not a random year-round event.

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

Follow-up questions

Frequently asked

Sources(4)

[1]
NFPA
Non-Home Electrical Fires report (Campbell, 2019) — arc-fault mechanism and ignition quote
[2]
NFPA
Home Fires Caused by Electrical Distribution and Lighting Equipment — arcing as heat source in 73% of such fires
[3]
USFA/FEMA
NFIRS Complete Reference Guide (2015) — confirms only a generic 'Animal' ignition-factor code, no rodent-specific code or percentage
[4]
Peer-reviewed cable-damage literature
Cogelia, LaVoie & Glahn — rodent incisor growth and cable-sheath damage thresholds, 25th International Wire and Cable Symposium

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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