How Many Smoke Detectors Do I Need?

Smoke detectors provide early warning of a house fire before flames get out of control, giving occupants critical time to get an extinguisher, evacuate, and call the fire department. You can integrate smoke detectors into your home security system, but for these devices to work efficiently, you'll need to install the recommended number of sensors in the right places.

Read on to learn more.

How many smoke detectors should I have in my home?

According to the National Fire Protection Association (NFPA), homeowners should follow these guidelines when installing smoke detectors:

• One per every level of the home (basement, first floor, second floor, etc.)
• One inside every bedroom
• One outside each sleeping area

Let's say you own a three-bedroom home with two stories and a basement. You'll need a total of six smoke detectors to make sure every area of your home is protected:

• One detector for the basement
• One detector for the first floor (living room and dining room)
• Four detectors for the second floor (one inside each bedroom plus one outside the bedroom doors)

Where to install smoke detectors

Smoke rises, so smoke detectors must be mounted high to work properly. The ideal spot is the ceiling, but you can also mount it on the wall, provided the detector is not more than 12 inches below the ceiling.

Placement guidelines differ slightly if your home has a pitched roof. You must place the smoke detector four inches away from the peak (the uppermost point where the two sides of the roof meet) but no more than three feet away from the peak.

Avoid placing smoke detectors in the kitchen and anywhere less than ten feet away from cooking appliances. Doing so can trigger false alarms and become a common nuisance. Similarly, smoke detectors should be far from drafty areas that can hinder the device's efficiency, like windows, doors, or ceiling fans.

How do smoke detectors work?

Smoke alarms identify potential fires by sensing small particles in the air using ionization, photoelectric technology, or both.

You can install battery-powered smoke detectors or hardwire the sensor to your home's electrical system. A hardwired smoke detector also has a 9-volt battery backup that will kick in if the power goes out.

A weakness of smoke detectors is that the alarm only goes off in the room where the smoke is detected. And if you're not within earshot, you may not hear the alarm in time. Interconnected smoke alarms leverage wireless connectivity to address this problem: if a single sensor is triggered, every device in the home will sound off.

Types of smoke detectors

Ionization

Ionization detectors ionize air inside the device using a small amount of radioactive material, creating a steady electrical current. In the event of a fire, smoke will enter the device's chamber, interfering with the electrical charge, reducing the current, and causing the alarm to go off.

Ionization smoke detectors are particularly sensitive to fast-burning, flaming fires such as those caused by paper or wood but may not respond as quickly to smoldering fires that produce less visible smoke.

Photoelectric

Photoelectric alarms sense home fires by detecting changes in the light inside the chamber. The device has a light source inside and a light-sensitive sensor that detects scattered light. When smoke enters the chamber, it scatters the light, causing some of it to be directed towards the sensor. This change in light intensity triggers the fire alarm.

This type of smoke alarm is particularly effective at detecting smoldering fires, which produce more visible smoke before bursting into flames. They are less sensitive to false alarms caused by cooking smoke or steam than ionization smoke detectors.

Combination or dual-sensor smoke alarm

Dual-sensor smoke detectors make for the most comprehensive fire safety system. These devices combine both ionization and photoelectric smoke detectors so the alarm will go off no matter what type of fire hazard starts in your home: a flaming, fast-burning fire or a smoldering slow burn.

Multi-sensor detectors

Multi-sensor detectors integrate not only dual-sensor smoke alarms but also heat and carbon monoxide (CO) detectors.

Carbon monoxide is an odorless and colorless gas produced by incomplete combustion of fuel. Since this gas has no smell, taste or color, it can build up to dangerous amounts indoors and occupants may not notice until they become dangerously ill. Furthermore, occupants may not know to seek help in a timely manner because early symptoms of CO poisoning often mimic the flu.

A carbon monoxide detector can catch CO buildup and help protect the health of you and other family members — particularly young children, older adults, smokers, and those with lung or heart disease.

Some smoke detectors also include heat sensors that detect rapid increases in temperature, such as those caused by a fire. Heat sensors are particularly useful in areas where smoke detectors may result in false alarms, such as the kitchen, garage or a designated smoking area.

Summary of Money's How Many Smoke Detectors Do I Need

To determine the number of smoke detectors you need, you'll need to assess your home's size, layout and local building codes. For the best protection in residential dwellings, the National Fire Protection Association set the following guidelines:

• One detector on every level of your home
• One detector inside each bedroom
• One detector per each sleeping area, placed in the hall outside the bedrooms
• One in the basement, if applicable