Map it floor by floor
Sketch each level with its bedrooms, existing alarms and fuel-burning appliances, then check it against two rules: one alarm on each level, and one in a central spot outside each separate sleeping area (U.S. Fire Administration). In a typical row, that works out like this:
- Third floor: in the hall or landing outside the bedrooms. If the top floor is one big bedroom, put it just outside that door.
- Second floor: in the hall that the front and back bedrooms open onto. Two bedrooms off one short hall can share one alarm; a bedroom at the far end of a long hall may need its own.
- First floor: a central spot such as the stair hall or the living room wall, not in the kitchen, which CPSC advises against.
- Basement: see the next section.
One alarm at the bottom of the stairs is not a whole-house plan. If you only have one for now, EPA says to put it near the sleeping areas and make sure it is loud enough to wake you (EPA placement FAQ).
Height and what to keep it away from
There is no single correct height. CPSC says CO alarms may go in a plug-in receptacle or high on the wall, and that plug-in or hardwired units should have battery backup. Keep them away from heating vents and anywhere furniture or curtains could cover them, and not directly above fuel-burning appliances (CPSC CO fact sheet). EPA adds the 15-foot distance from any fuel-burning appliance (EPA placement guidance).
In a narrow row, measure that 15 feet with a tape rather than guessing, especially on the first floor near the basement stair or a gas range. If no spot on a level meets both the 15-foot distance and the booklet’s rules, ask the manufacturer or the fire department before you settle on a closer one.
The basement: the one question federal guidance splits on
EPA counts the basement as part of the home’s livable space and includes it in every-level coverage. CPSC’s CO alarm page says not to install CO alarms in basements unless they include a sleeping area (EPA placement guidance; CPSC CO alarms page). A practical way to decide: if anyone sleeps, works or spends hours down there, treat it as a living level and give it an alarm that meets the 15-foot distance. If it holds only the furnace, water heater and laundry, make sure the first-floor alarm near the basement door is solid, and ask your fire department where it wants basement coverage for your layout. Either way, not right over the boiler.
Interconnection and power
Interconnected alarms give the best protection. A licensed electrician can install hardwired interconnected CO alarms, or you can use wireless, plug-in or battery alarms (NFPA fast facts). If you go hardwired, ask the electrician whether the job needs an L&I electrical permit; the rules are in when electrical work in a Philadelphia home needs an L&I permit.
Test each alarm monthly (EPA placement guidance), and once have someone listen from each bed with the bedroom doors shut the way they are at night. Alarms also wear out; see how often smoke and CO alarms should be replaced.
Low-level CO monitors are extras, not substitutes
CPSC describes household CO alarms as life-safety devices that are not meant to protect against low-level exposure, and it recommends alarms that meet the UL 2034 standard (CPSC on CO alarms and low-level exposure; CPSC CO fact sheet). EPA notes that low-cost air monitors are not designed or certified the way CO alarms are to warn of immediate danger (EPA on low-cost monitors). Add a monitor if you want one, but never take down a listed alarm because a screen shows a number.
Pennsylvania and Philadelphia specifics
Pennsylvania’s Carbon Monoxide Alarm Standards Act (Act 121 of 2013) defines a residential building to include “multiple single-family dwellings which are not more than three stories in height with a separate means of egress,” which describes most rowhomes. For those homes, the law does not order you to install alarms; it requires the seller to disclose CO detector installation on the property disclosure statement. The installation requirement, a centrally located alarm near the bedrooms and the fuel-burning heater or fireplace, applies to apartments in buildings with three or more units that have fuel-burning appliances, a fireplace or an attached garage (Act 121 text).
If an alarm goes off, get everyone outside and call 911 from there. Philadelphia’s Office of Emergency Management also says to call your local utility (Philadelphia OEM); PGW’s 24-hour emergency line is 215-235-1212 (PGW safety page). What happens next, and when you can go back in, is covered in when a CO alarm means leave the house. Once things are safe, a heating tech can check whether a flue is spilling exhaust; see how to check for flue backdrafting.