Carbon monoxide alarm laws: when techs must install

Why this lands on the HVAC tech

Each year more than 400 Americans die from unintentional carbon monoxide poisoning not linked to fires, more than 100,000 visit an emergency department and more than 14,000 are hospitalized, and gas and oil furnaces are among the sources^[4]. Natural gas was used in 58% of US homes in 2020^[3]. The person most likely to stand next to a fuel-burning appliance and look at the alarm situation is your technician.

That makes CO alarm law a practical question for HVAC, water heater, fireplace and generator work: when does your install trigger a legal requirement, when are you only recommending, and what should the tech write on the invoice? This guide covers the state-law side. For what CSRs say when a customer calls with an alarm going off, see the separate CO alarm call protocol.

How state requirements are built

The National Conference of State Legislatures, in a summary updated September 29, 2025, says most states have adopted requirements mandating CO detectors, through statute, regulation or code^[1]. The differences are in what triggers the requirement and where alarms must go. NCSL groups the common triggers as^[1]:

• A fuel-burning appliance or heater in the home.
• An attached garage.
• A sale or transfer of the property.
• Renovation of the dwelling.
• New construction after a set date.
• Rental units, where the landlord must provide alarms.

Examples from state law

Two details stand out for techs. Distance rules differ: Illinois uses 15 feet from each sleeping room, Minnesota ten feet^[1]. And many requirements fall on the owner or landlord, not the contractor, which shapes what your tech can and cannot insist on during a service call.

Three situations your techs meet

Sort your policy by what the tech is doing in the home:

1. Installing or replacing a fuel-burning appliance under a permit. Ask your local permit office or inspector whether alarms must be present or added as a condition of final inspection. Where they must, quote the alarms in the job and install them before the inspection.
2. Servicing a fuel-burning appliance with no alarm present. Recommend an alarm on every level and outside sleeping areas, in line with CPSC advice^[2]. Offer to install one if you carry them. Record the recommendation.
3. Finding an alarm that is old, unplugged or missing its battery. Point it out, show the customer the date on the back and recommend replacement based on the manufacturer's stated replacement age, which CPSC notes appears in the product literature^[2].

In rental homes, tell the tenant what you found and note it on the work order for the landlord or property manager, since the duty usually sits with the owner.

A 60-second alarm check on every gas call

1. 01

   Ask before you start

   "Do you have carbon monoxide alarms, and where are they?" Customers often confuse smoke and CO alarms; ask to see the label.

2. 02

   Look at one alarm

   Check that it is a CO or combination alarm, that it is powered and that the manufacture date is within its stated life. Look for the UL 2034 listing CPSC recommends^[2].

3. 03

   Count levels and sleeping areas

   Note whether every level and the area outside bedrooms has coverage.

4. 04

   Recommend in plain words

   "I'd recommend one on this floor and one outside the bedrooms. I can put them in today if you'd like."

5. 05

   Record it

   Add a line to the invoice or job notes: alarms present or absent, condition and what you recommended.

Stocking and installing alarms

If your techs recommend alarms, they should be able to install one on the spot. A customer who agrees at the kitchen table often forgets once the truck leaves. Keep the choice simple so every tech installs the same way:

• Carry one plug-in model with battery backup and one battery-only model, both listed to UL 2034, so every home has an option^[2].
• Use combination smoke and CO alarms only where the customer understands they replace an existing smoke alarm and the local code allows it.
• Follow the manufacturer's placement instructions, which usually warn against mounting right next to fuel-burning appliances, in bathrooms or in dead-air corners.
• Write the install date on the back of every alarm and in the job notes, so the next tech knows when it is due for replacement.
• Test the alarm with the customer watching, and show them what the CO alarm sounds like compared with the smoke alarm.

Hard-wired and interconnected alarms are electrical work. In many places they need a licensed electrician or an electrical permit, so route those requests to the right trade rather than having an HVAC tech splice into a circuit.

Landlords, property managers and home sales

Because many state requirements apply to rentals and to homes being sold^[1], property managers and real estate transactions are where alarm questions come up most. A property manager may ask your tech to confirm alarms during a furnace service so the owner can show compliance. A seller may call a week before closing because an inspector or buyer asked about CO alarms.

1. For property managers, add an optional "CO alarm check and replace" line to your maintenance agreement, with the alarm count per unit spelled out.
2. Photograph each alarm you install or check in a rental, with the unit number in the frame, and attach the photos to the work order.
3. For pre-sale requests, ask which state rule the agent or inspector is citing, then install to that requirement and to CPSC placement advice.
4. Never sign a statement that a home "complies with state CO law." Describe what you installed and where; the owner or their agent decides compliance.

That last point matters. Your record should be factual: number of alarms, models, locations and install date. It protects your company if the requirement is disputed later and keeps your tech from giving legal opinions in someone's hallway.

What techs can say

• "Your furnace is working safely today, but you don't have a carbon monoxide alarm on this level. CO has no smell, so an alarm is the only warning."
• "This alarm is past the replacement age printed on the back. It may not sound when it should."
• "Your state may require alarms when a home is sold or rented. If you're planning either, it's worth adding them now."
• "I'd also suggest a yearly inspection of the heating system; it's the main thing that keeps CO from being a problem in the first place."

CPSC recommends having the heating system professionally inspected and serviced every year^[2]. That advice fits naturally into a maintenance plan conversation without sounding like a sales pitch.

Generators, outages and seasonal risk

CO risk rises with weather. CPSC staff counted at least 94 generator-related CO deaths in 2005, and 47 of them occurred during power outages caused by severe weather^[2]. If your company installs standby generators or sees a spike in no-heat calls during storms, make the alarm check part of those jobs too, and include alarm advice in any storm-season customer messages.

Example: building it into the job

Example: a fictional six-tech HVAC company adds a mandatory CO alarm field to its digital work order for every gas furnace, boiler and water heater visit, with three options: present and current, present but expired, absent. Techs carry two combination alarms on each truck. Over a heating season the owner can see which neighborhoods have the most missing alarms and uses that to time a fall safety reminder to maintenance members. When an inspector asks about alarms on a permitted furnace change-out, the work order already shows what was installed and where.