Frequently asked questions
The 19 questions we are asked most, answered with the code section or the standard behind them — and a link to the page that covers each one properly.
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Smoke alarms
How many smoke detectors do I need?
One inside each sleeping room, one outside each separate sleeping area in the immediate vicinity of the bedrooms, and one on every level of the home including the basement — the three requirements NFPA 72 sets out for dwellings. For a typical three-bedroom two-story house with a basement that is six alarms. The full arithmetic, including split-levels and open plans.
How far does a smoke alarm have to be from the stove?
At least 10 ft. NFPA 72 (2025) §29.11.3.4 excludes alarms from a 10 ft radial distance along a horizontal flow path from a stationary or fixed cooking appliance, and between 10 and 20 ft the alarm must have a silencing means or photoelectric sensing and be listed for resistance to common cooking nuisance sources. Kitchen and bathroom placement.
Photoelectric or ionization — which should I buy?
Photoelectric for a home. It responds sooner to smoldering fires, which are the ones that kill people while they sleep, and it nuisance-trips far less on cooking aerosols. Dual-sensor units cover both mechanisms. Why the mechanism matters.
How long do smoke alarms last?
Ten years from the date of manufacture stamped on the back — not ten years from installation. The sensing chamber degrades whether or not the alarm has ever been triggered, and the test button only confirms the horn and the battery. Where to find the date.
Why does my smoke alarm chirp when the battery is new?
Usually because it has reached end of life and is signaling that rather than a low battery. Other causes are a battery drawer not fully latched, a dirty sensing chamber, or a unit that needs its alarm memory cleared. Check the manufacture date first. The full diagnostic sequence.
Why does my smoke alarm go off for no reason?
Nearly always position, not a fault. The common causes are an ionization alarm too close to a cooker, an alarm within 36 in of a bathroom door or a supply register, steam, dust, or insects in the chamber. Moving the alarm fixes far more of these than replacing it does. Diagnosing nuisance alarms.
Can I put a smoke alarm near a ceiling fan?
Not within 36 in of the fan blades. Moving air disturbs the smoke flow the sensor depends on, so NFPA 72 excludes that zone. In a bedroom with a central fan the alarm moves off-center, which is correct rather than a compromise. Sloped ceilings and other awkward cases.
Carbon monoxide
Should a carbon monoxide detector be high or low?
Follow the manufacturer's instructions for your specific unit. CO mixes with air rather than reliably rising or sinking, which is why there is no single satisfying answer. In practice: within earshot of the bedrooms, at least one per level, avoiding dead air within about 6 in of a ceiling-wall corner and avoiding positions directly above a fuel-burning appliance. Room by room.
Do I need a CO detector if I don't have gas?
Often yes. An attached garage, a fireplace, a portable generator during an outage or a shared wall with another dwelling can all put CO into an all-electric home. A genuinely detached all-electric home with no garage, no fireplace and no generator is the one case where the answer may be no. The honest version.
Why won't my CO alarm warn me about low levels?
Because UL 2034 forbids it. A listed residential alarm must not alarm below 30 ppm, and its response requirements are 70 ppm within 60 to 240 minutes, 150 ppm within 10 to 50 minutes and 400 ppm within 4 to 15 minutes. It is designed to prevent acute poisoning, not to report air quality. Why low-level monitors exist.
What are the symptoms of carbon monoxide poisoning?
Headache, dizziness, weakness, nausea, vomiting, chest pain and confusion — a pattern that resembles flu without the fever, and that often improves when you leave the building. If you suspect it, get everyone outside into fresh air and call 911 from outside. The full symptom guide.
Extinguishers and blankets
What kind of fire extinguisher should a house have?
A multi-purpose ABC dry chemical extinguisher rated at least 2-A:10-B:C, rechargeable, with a metal valve, mounted near the kitchen exit rather than beside the cooker. Add a second, larger unit in a garage or workshop. Our picks and the reasoning.
What do the numbers on a fire extinguisher mean?
They are relative capability ratings from the UL fire tests. The number before A relates to the size of wood-crib fire the unit can extinguish and the number before B to the square footage of flammable-liquid fire. There is no number before C — that letter simply certifies the agent is safe around live electrical equipment. The full class reference.
How do you put out a grease fire?
Never with water — water flashes to steam beneath the oil and throws burning fuel out of the pan. Turn off the heat if you can reach the control safely, cover the pan with a fire blanket or a metal lid, and leave it covered for at least half an hour. Do not move the pan. The step-by-step, and when to leave instead.
Is a fire blanket better than a fire extinguisher?
For a contained pan fire, yes: faster, nothing to aim, no corrosive residue. For anything that has spread beyond its container, no, because a blanket has no range. Most kitchens want both, in different positions. Where each one fails.
Are fire blankets toxic?
Not in the poisonous sense — woven fiberglass is chemically stable and does not off-gas. It does shed short glass fibers when handled, and those irritate skin and airways. Gloves, minimal handling and bagging a used blanket deal with it. The exposure question in full.
Is fire extinguisher powder toxic?
ABC dry chemical is monoammonium phosphate: an irritant rather than an acute poison, unpleasant to breathe, corrosive to metal and electronics, and a genuine problem for pets and reptiles. Ventilate, clean thoroughly, and keep animals away from the residue. What the safety data actually says.
Getting out
What length escape ladder do I need for a 2-story house?
Usually 13 to 14 ft, but measure rather than assume — from the window sill to the ground, at the window you would actually use. Deep floor joists, a raised foundation or a sloping garden can each add a couple of feet. Two-story ladder picks.
Do I need an escape ladder in every bedroom?
In every upstairs bedroom without a second exit, yes. You cannot cross a landing that is on fire to fetch a ladder from another room, so a ladder stored anywhere except the room it serves cannot be relied on. Why permanent installations solve part of this.
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