What's the most common pest found in a furnace or boiler room, and why?

Firebrats are the standout, because a furnace or boiler room offers exactly the sustained high heat they prefer — University of Maryland Extension describes them as characteristically found around ovens, heating units, fireplaces, hot water pipes, and near the furnace in winter, with a temperature optimum around 100 degrees Fahrenheit according to University of Missouri Extension. Unlike silverfish, which prefer cooler, damp spots away from heat, firebrats specifically seek out the hottest, driest-to-moist microclimate in a basement, which is almost always the immediate area around active heating equipment running continuously through a long winter.

Are rodents also drawn to furnace and boiler rooms, or mainly insects?

Both, for related but distinct reasons. Rodents nest in the voids and cabinet spaces adjacent to furnaces and boilers because the area offers stable, continuous warmth and shelter from disturbance, the same general draw that pulls them toward any warm equipment zone in a house. Firebrats occupy the immediate cracks and surfaces closest to the hottest pipes and equipment surfaces themselves. It's common for a boiler room to have both kinds of activity at once, which is part of why professional identification matters — the control approach for firebrats is entirely different from rodent exclusion and nest removal.

When does a boiler-room pest issue become a carbon monoxide concern?

Specifically when nesting material, debris, or a rodent nest ends up in or around the flue, vent, or chimney pathway that carries combustion gases out of the home. A blocked or partially blocked flue can force carbon monoxide back into living space instead of venting it outside, which is a genuine safety issue rather than a routine pest nuisance. The CDC recommends annual chimney and flue inspection specifically because debris blockage is a documented cause of CO buildup, and any furnace or boiler room pest inspection should include a look at the venting path as a standard precaution, not an afterthought.

What should I check myself before calling a professional about boiler-room pests?

A visual check for visible insects on walls or near pipes, small droppings along baseboards or in corners, or any obvious debris or nesting material near a flue or chimney base gives a professional a head start, but climbing into flue or vent openings yourself isn't advisable. Confirming that carbon monoxide alarms are present and functioning is a reasonable baseline safety step regardless of whether pests are involved. Beyond that, the identification and control work — distinguishing firebrats from silverfish, assessing rodent nesting, and checking the venting path for obstruction — is best left to a professional inspection.

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

What Pests Infest Furnaces or Boiler Rooms?

Heat draws them in

Furnace and boiler rooms are among the warmest, most sheltered spots in a New Hampshire home, and they draw heat-seeking pests: firebrats above all, thriving above 90°F near the equipment, plus warmth-seeking rodents nesting in adjacent voids, and occasional silverfish or camel crickets where moisture is also present.

Mostly nuisance. The one genuine safety escalation is a nest or debris blocking a flue or vent, which is real but rationed to that specific case.

At a glance

The mechanism: Heat draws them in
Who fixes it: A licensed pest pro
The rest lives at: What role do HVAC systems have in winter pest prevention?

Cause, or just reveal?

Heat draws them in

Mostly nuisance. The one genuine safety escalation is a nest or debris blocking a flue or vent, which is real but rationed to that specific case.

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 furnace or boiler radiates continuous heat, so heat-loving firebrats colonize cracks and voids in the room while rodents nest nearby. In some cases nests or debris accumulate in or around flue, vent, or chimney pathways, and if a flue becomes obstructed, combustion gases including carbon monoxide can be forced back into the home instead of venting outside. The CDC advises having chimneys checked and cleaned annually because they can be blocked by debris, which can cause carbon monoxide to build up inside a home.

Source:CDC— "Carbon Monoxide Poisoning Basics" — chimneys blocked by debris cause CO buildup; recommends annual inspection

The honest router

Is this an HVAC problem or a pest problem?

Who actually fixes it

A licensed pest pro

Identifying which pest is present and controlling it — firebrat and silverfish control is routine work distinct from rodent exclusion — is the core job for a pest professional.

Escalate when

Any sign of a blocked flue or vent, or rodent nesting in the venting path, turns up — that's an immediate HVAC technician or chimney-professional matter, and working carbon monoxide alarms should be confirmed as a baseline safety step regardless.

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 what infests furnace and boiler rooms and why. Broader overwintering and occasional-invader behavior belongs to our winter pests hub; equipment-damage and safety severity belong to our pest damage and risks hub.

What role do HVAC systems have in winter pest prevention?

Can bird nests cause chimney fires?

Local to New Hampshire

How this calibrates for NH

New Hampshire context

With oil and gas heating dominant across New Hampshire and long burn seasons the norm, boiler and furnace rooms stay hot for months, creating ideal firebrat habitat, and annual pre-season flue and vent inspection is especially important given the state's heavy reliance on combustion heating through a long winter.

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

Follow-up questions

Frequently asked

Sources(3)

[1]
University of Maryland Extension
"Silverfish and Firebrats" — firebrats near furnace in winter
[2]
University of Missouri Extension
"Silverfish and Firebrats" (G7376) — firebrat temperature optimum ~100°F; boiler rooms/hot water heaters
[3]
CDC
"Carbon Monoxide Poisoning Basics" — chimneys blocked by debris cause CO buildup, annual inspection

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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