Carbon Monoxide Leak in an Apartment: What to Do

You are settling in for the evening when your CO alarm starts blaring — loud, repeating beeps, not the quiet chirp you are used to. You live on the third floor of an apartment building and you do not even have a gas stove. Where is the CO coming from? In multifamily buildings, carbon monoxide can originate from your unit, a shared boiler room, an attached parking garage, or even a neighbor's malfunctioning appliance — and it can travel through wall cavities, utility chases, and ventilation pathways. The source does not have to be in your apartment for the danger to be real. This page gives apartment-specific emergency steps, explains who to contact, and covers what should happen after the immediate crisis.

Quick Safety Summary

• If a CO alarm activates in your apartment, treat it as real — leave immediately with everyone (including pets).
• CO is odorless — "I don't smell gas" does not mean it is safe.
• Notify building management and neighbors — CO can affect multiple units.
• Do not re-enter until authorities or a qualified technician confirm the building is safe.
• Document everything: date, time, alarm model, symptoms, and official readings for follow-up.

Step-by-Step: What to Do Right Now

For the expanded emergency checklist: what to do if a CO alarm goes off.

What Not to Do

• Don't ignore it because you "don't smell gas." CO has no smell. The odorant you associate with gas leaks (rotten eggs) is added to natural gas — it is a different hazard.
• Don't stay inside to "air it out" if anyone has symptoms.
• Don't assume it is a false alarm until it is verified by someone with a calibrated meter.
• Don't silence the alarm and go back to sleep. If the alarm activated (not just a maintenance chirp), it detected something. For chirp vs alarm patterns, see CO detector beeping.

Where Apartment CO Can Come From

In a single-family home, the CO source is almost always inside your own building. In apartments, the possibilities are wider:

• Shared boiler or furnace room — combustion gases can enter units through vents and utility chases.
• Attached or underground parking garage — vehicle exhaust can infiltrate upper floors through stairwells, elevator shafts, and gaps in the structure.
• A neighbor's appliance — a malfunctioning gas stove, water heater, or unvented space heater in an adjacent unit.
• Backdrafting from shared venting — when exhaust that should go up the flue is pulled back into the building by wind or pressure imbalances.
• Construction or renovation nearby — fuel-burning equipment used during work on the building or adjacent properties.

Because the source may be outside your control, building-level investigation is essential. A CO alarm in your unit does not necessarily mean your appliances are the problem — but it does mean something in the building is producing or channeling CO into your living space.

Who to Call: Practical Contact Order

1. Emergency services (fire department) — if anyone has symptoms, if the alarm is sounding, or if you cannot quickly identify a safe cause.
2. Building management or security — to check shared boilers, garages, vents, and other common sources. They may need to evacuate other units.
3. Licensed HVAC technician — to inspect your furnace, water heater, stove, and venting after the immediate emergency is resolved.
4. Your utility company — if a gas leak is also suspected (rotten egg smell in addition to the CO alarm).

After the Emergency: Inspection, Documentation, and Prevention

Once the immediate danger is addressed, focus on preventing repeat events. In multifamily buildings, root causes may involve shared venting, backdrafting, mechanical room issues, or garage exhaust infiltration.

Document everything

• Date and time of the alarm activation.
• Which alarms activated and in which rooms.
• Symptoms experienced by anyone in the unit.
• Any official CO readings provided by responders.
• Photos of the alarm model, display messages, or error codes.

Request written follow-up

Ask building management for written confirmation of inspections and repairs. This is important for your records and may be relevant if the issue recurs or if you need to involve local housing authorities.

Review your CO alarm setup

Replace any alarm that is past its end-of-life date. Verify placement near sleeping areas and on every occupied level of your unit. For planning, see how many CO detectors do I need and where to place a CO detector.

Renter Rights and Landlord Responsibilities

Many jurisdictions require landlords to install compliant CO alarms before occupancy and maintain them to a specified standard. Tenants are often expected to test alarms and report issues, but replacement responsibility varies by local law and lease terms. If your building does not have CO alarms or if management dismisses a real alarm event, check your local building code and fire department resources for reporting options.

A practical approach that reduces risk regardless of who is technically responsible: test your alarms monthly, report chirps and faults to management in writing (email creates a paper trail), and keep at least one battery-powered CO alarm in your unit even if the building provides hardwired units. During a power outage — when heating risks rise — hardwired alarms without battery backup go silent exactly when you need them most.

Sources & References

• CPSC: Carbon Monoxide Information Center
• CDC: Carbon Monoxide Poisoning Prevention
• NFPA: Carbon Monoxide Safety

Published: January 15, 2024