Carbon Monoxide and Your Chimney: What Rochester Homeowners Must Know

If your carbon monoxide alarm is sounding right now: get everyone out of the house immediately, call 911 from outside, and do not re-enter until emergency responders have cleared the building. CO is colorless, odorless, and can incapacitate before you feel seriously ill — never try to "find the source" while an alarm is active. Once the house is safe, the question becomes why it went off, and for Rochester homeowners, the chimney system is one of the first places to look.

Many homeowners asking "why does my CO detector go off?" assume the furnace is at fault. Sometimes it is. But the chimney and venting system — the path combustion gases take to leave your home — is just as often the problem, especially in Rochester's stock of 19th- and early-20th-century brick houses with older, sometimes unlined flues.

If Your CO Alarm Sounds: The Emergency Steps

This comes first because nothing else in this article matters if it's read during an active alarm. The sequence from fire-safety guidance is simple:

• Get everyone out. All people and pets, immediately. Don't stop to open windows, find the source, or silence the alarm.
• Call 911 from outside. The fire department will meter the air, find the source, and tell you when — or whether — it's safe to re-enter.
• Do not re-enter until cleared. CO dissipates unevenly; a house that "smells fine" can still hold dangerous concentrations, especially in bedrooms and basements.
• Watch for symptoms. Headache, dizziness, nausea, confusion, and fatigue that improve when you leave the house are classic CO exposure signs. Seek medical attention if anyone feels unwell — CO poisoning is frequently misread as flu, and Rochester's long heating season overlaps flu season.

Never assume a sounding alarm is a false alarm or a dying battery. A low-battery chirp is a short, single beep every 30–60 seconds; an alarm is a loud, repeating pattern. If you can't tell the difference, treat it as an alarm.

How a Chimney Puts CO Into Your Home

Every fuel-burning appliance — furnace, boiler, water heater, fireplace, wood stove — produces carbon monoxide. In a healthy system, the chimney's draft carries all of it up and out. CO enters living space when that venting path fails, in one of three ways:

• A blocked flue. Bird and squirrel nests, fallen leaves, deteriorated mortar fragments, and collapsed clay flue tiles can partially or fully obstruct a flue. With nowhere to go, combustion gases spill back into the house. A blockage in the furnace flue is particularly dangerous because the appliance runs unattended, often at night.
• A cracked or deteriorated liner. The liner is the sealed channel inside the masonry. When tiles crack or joints open — common on Rochester stacks after decades of freeze-thaw cycling — exhaust can leak into the chimney cavity and migrate through porous brick into rooms. This pathway is invisible from inside and outside; it's typically found only by a camera inspection of the flue.
• Backdrafting. Instead of rising, flue gases flow backward down the chimney and out of the appliance or fireplace. The most common modern trigger is a tightened house: new windows, added insulation, kitchen and bath exhaust fans, and a new high-efficiency furnace can leave the home so depressurized that air is pulled down the chimney. A fireplace or furnace that vented fine for decades can start backdrafting the week after a weatherization project.

Appliance-side failures — a cracked heat exchanger, a misadjusted burner — also produce CO, which is why post-event diagnosis should cover both the appliances and the venting system, not one or the other.

Why Rochester Homes Are Especially at Risk

Three local realities stack the odds. First, the housing stock: neighborhoods like the 19th Ward, Corn Hill, Park Avenue, and Maplewood are dominated by brick homes built between the 1850s and 1930s. Many still vent through original clay-tile-lined flues — and some through flues with no liner at all. Second, the climate: lake-effect winters off Lake Ontario mean more than 100 freeze-thaw cycles in a bad year. Water enters mortar joints and liner cracks, freezes, expands, and widens them a little more each season. Third, the pattern of upgrades: Rochester's older homes have almost all been re-furnaced, re-windowed, and re-insulated at least once, and each project changed the house's air balance without anyone re-checking whether the chimney still drafts.

Multi-flue stacks add another wrinkle. A single chimney may carry the furnace flue, a fireplace flue, and an abandoned third run. A blockage or liner failure in one flue can affect the draft of its neighbor, and abandoned openings capped decades ago sometimes communicate with living space through gaps in the masonry.

What to Do After a CO Alarm Event

Once the fire department has cleared the house, treat the event as a diagnostic starting point rather than a scare that's over:

• Don't restart fuel-burning appliances — furnace, water heater, fireplace — until they've been checked. The FD reading tells you the house is clear; it doesn't tell you what failed.
• Have the heating appliances serviced by a licensed HVAC technician, and have the chimney system inspected by a certified chimney sweep. A Level 2 camera inspection is the appropriate standard after a venting malfunction under NFPA 211 — it's the only way to see cracked liner tiles and blockages inside the flue.
• Tell the sweep what changed recently. New windows, new furnace, added insulation, a kitchen exhaust upgrade — these details point directly at backdrafting causes.
• Check detector placement. CO alarms belong on every level of the home and outside sleeping areas, per manufacturer's instructions — not inside the fireplace room only. Replace units past their rated service life.
• Expect a ballpark cost. In Rochester, a Level 2 chimney inspection with camera typically runs an estimated $200–$500; minor fixes like a new cap or cleared blockage are modest, while relining a failed flue is a larger project quoted after inspection.

Frequently Asked Questions

Related Pages

For service coverage across the city, visit the Rochester chimney services hub or browse the city-wide chimney FAQ. Neighborhood pages: 19th Ward, Corn Hill, and Maplewood. Continue reading: Smoke Backing Into Your Room: 5 Common Causes and What Is a Level 2 Chimney Inspection?.