Carbon Monoxide Alarm Rules When You Replace a Furnace

If your home has a gas, oil or propane furnace, a fireplace or an attached garage, the law almost certainly requires working carbon monoxide alarms, and a furnace replacement is the moment an inspector or installer is most likely to check. In Ontario the rule is a CO alarm next to every sleeping area. In most US states that follow the International Residential Code, a permitted furnace swap triggers CO alarms outside each bedroom area even in an older house.

The details change by province, state and city. Below are the main rules across Canada and the US, where the alarms go, and what to settle before installation day.

Why the furnace swap is the trigger

A fuel-burning furnace is the most common source of carbon monoxide in a house. A cracked heat exchanger, a blocked vent, a poorly sealed sidewall termination or a backdrafting water heater sharing an old chimney can all push CO into living space. Replacing the furnace changes the venting, and can leave the water heater alone in a chimney that is now too big for it.

Codes treat that work as a permitted alteration, and once a permit is open, many inspectors look for CO alarms before signing off.

Ontario: the Fire Code applies to every home

Ontario has the clearest rule in Canada. Since October 2014, the Ontario Fire Code (Division B, Section 2.16) has required CO alarms in every residential building that contains a fuel-burning appliance, a fireplace or an attached garage. The change came from the Hawkins-Gignac Act, passed after a family in Woodstock died from carbon monoxide in 2008.

What that means for a house:

• A CO alarm must be installed adjacent to each sleeping area.
• The rule applies to existing homes, not only new ones, so a 1970s bungalow in Hamilton is covered the same way as a new build in Vaughan.
• In apartment and condo buildings, alarms are also required in the service room that holds a fuel-burning appliance and in suites that share a wall, floor or ceiling with that room or with a storage garage.
• Landlords are responsible for installing and maintaining the alarms in rental units, and tenants must tell the landlord when one stops working.

The Ontario Building Code adds hardwired alarm requirements for new construction and major renovations. Our Toronto service area page covers the HVAC work we scope across the city.

Quebec and the rest of Canada

The National Building Code of Canada requires CO alarms in new homes that have a fuel-burning appliance or an attached storage garage, and the provinces that adopt it carry that requirement into their own codes. Quebec's Construction Code, Chapter I (Building), includes a similar requirement for new residential construction.

For existing homes outside Ontario, the rule usually comes from a municipal bylaw or provincial fire code, and coverage is uneven: some cities cover every dwelling with a fuel-burning appliance, others only rentals or new builds. Install them anyway, since an alarm costs little next to a new furnace.

In Canada, look for alarms certified to CSA 6.19. In Quebec, the gas side of the job must be done by a licensed contractor, and in Ontario by a TSSA-certified gas technician, which is also who should run the combustion test on the new unit.

The US model code: IRC section R315

Most US states build their residential code on the International Residential Code. Section R315 covers carbon monoxide alarms and has two parts that matter here:

• New construction: dwellings with fuel-fired appliances or an attached garage need CO alarms outside each separate sleeping area, close to the bedrooms, and inside any bedroom that has a fuel-burning appliance in it or in its attached bathroom.
• Existing homes: when alterations, repairs or additions that need a permit happen in a home with a fuel-fired appliance or attached garage, the home must be brought up to the same alarm locations as a new house.

The exceptions for existing homes cover work like roofing, siding and decks, and mechanical work on systems that do not burn fuel. A gas furnace burns fuel, so its replacement normally falls inside the rule. Your jurisdiction may use an older edition or local amendments, so check what your building department has adopted.

The IRC allows battery-powered alarms in existing homes where hardwiring would mean opening walls or ceilings, unless there is attic or crawlspace access that makes running wire practical. In the US, alarms should be listed to UL 2034.

State laws that go further

Several states passed their own CO laws that apply to existing homes regardless of any permit:

• California: the Carbon Monoxide Poisoning Prevention Act of 2010 (SB 183) requires CO devices in every dwelling unit with a fossil-fuel appliance, fireplace or attached garage. Single-family homes had to comply by July 2011 and other dwellings by January 2013.
• New York: Amanda's Law requires CO alarms in one- and two-family homes and multiple dwellings that have fuel-burning appliances or systems. New York City has its own requirements under the city housing and building codes.
• Illinois: the Carbon Monoxide Alarm Detector Act requires an approved alarm within 15 feet of every room used for sleeping in homes with a fossil-fuel heater, appliance, fireplace or attached garage.
• Massachusetts: Nicole's Law requires CO alarms on every level of a home that has fossil-fuel equipment or an enclosed parking area.

Where the alarms go

Codes vary, but the placement rules overlap enough that one layout satisfies most of them:

1. One alarm in the hallway outside each group of bedrooms, close enough to wake people behind closed doors.
2. One on every level of the home, including the basement where the furnace sits (required in Massachusetts and Ontario apartment service rooms, recommended everywhere else).
3. One inside any bedroom that has a fuel-burning appliance in it or in an attached bathroom.
4. Follow the manufacturer's spacing from the furnace, water heater, kitchen range and bathrooms. Placing a CO alarm right next to the furnace can cause nuisance alarms during startup.

Interconnected alarms are required in many new-construction codes and worth adding even where they are not. Most CO alarms have a service life of 5 to 10 years and chirp at end of life. Check the date on the back of any alarm you already own.

What to settle before installation day

A furnace replacement is easier to close out when these points are handled up front:

• Ask who pulls the permit. The installing contractor normally does. Confirm it is on the quote.
• Ask about the alarms. Some contractors supply and mount them, others expect the homeowner to have them in place before the inspection. Either way, put it in writing.
• Ask about the water heater. If the new high-efficiency furnace vents out the side wall and the water heater stays in the old chimney, the chimney may need a liner. A water heater that backdrafts is a CO risk on its own.
• Ask for the combustion test results. A proper start-up includes checking CO in the flue gas and draft, and the readings belong in your paperwork.

Our furnace installation service includes sizing, venting and start-up checks, and the scope we send spells out who handles the alarms and the permit. If you are still choosing equipment, the guide to single-stage, two-stage and modulating furnaces explains the trade-offs.

Frequently asked questions

Is a carbon monoxide detector required when a furnace is replaced?

In most places, yes. Ontario requires CO alarms next to every sleeping area in any home with a fuel-burning appliance, whether or not work is being done. In US jurisdictions that follow the IRC, a permitted gas furnace replacement triggers CO alarm requirements in an existing home. Some Canadian cities and US counties have their own rules, so confirm with the local building department.

Can a furnace inspection fail because of missing CO alarms?

It can. In jurisdictions using IRC section R315, the alarms are part of the requirements tied to the permit, and many inspectors check them during the mechanical final. A missing or expired alarm can delay sign-off until it is installed.

Do CO alarms need to be hardwired?

Not always. New construction usually needs hardwired alarms with battery backup, often interconnected. In existing homes, both the IRC and Ontario's Fire Code accept battery or plug-in alarms in most cases, unless the renovation opens walls or ceilings and makes wiring practical.

Get a furnace quote that covers the details

A new furnace should arrive with the venting, the permit and the safety items already worked out. Tell us about your home and current system and we will send a written scope that covers the equipment, the venting changes and who handles the carbon monoxide alarms.