Understanding Smoke and Carbon Monoxide Detectors | Ask This Old House

In this video, This Old House master electrician Heath Eastman teaches host Kevin O'Connor everything he needs to know about these fire safety devices.

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Master electrician Heath Eastman shows Kevin O'Connor everything he needs to know about smoke and carbon monoxide detectors. The two discuss the different types of smoke detectors available and how they operate and interconnect. Then, Heath shows Kevin the difference between a smoke detector and a carbon monoxide detector, highlighting the importance of having both in a home.

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Two Types of Smoke Detectors
There are two types of smoke detectors: ionization and photoelectric. These devices will activate in the presence of smoke, but they both specialize in a particular type of combustion. Photoelectric detectors will detect smoldering fires sooner than ionization detectors, whereas ionization detectors will react sooner to flames.

Each box (and the back of each device) will indicate which type of detector it is.

Location Matters
When choosing a smoke detector, the area in the home makes a difference. For example, a steamy shower can set off an ionization detector in the hallway outside the bathroom. A photoelectric detector is a better choice for that area. The same would apply to kitchens or anywhere moisture may be present. However, mixing and matching photoelectric and ionization detectors throughout the home is fine.

Ask the AHJ
The AHJ (Authority Having Jurisdiction) [https://bit.ly/3w4zjR3] is the best source for information about how many smoke detectors are necessary and where to put them. In most cities, the AHJ is the fire department, but the building department might also oversee these regulations.

Manufacturer Date
It's important to know how old a smoke detector is, so manufacturers label the back of each device with a manufacture date. Detectors older than 10 years should be replaced, regardless of whether they still appear to be working.

Battery vs. Hardwired
Battery-operated smoke detectors are easy to install and can go anywhere the homeowner needs one. However, these devices typically alert individually, which means an activation for one device will not trigger the others.

Conversely, many local codes now require hardwired detectors. These detectors plug into the home's fire alarm system, providing constant power while still having a battery backup. When these devices alert, they will typically activate all of the smoke detectors in the home. However, each device needs an alarm wire run to the device's location, making these models much more difficult to install.

Carbon Monoxide Detectors are Just as Important
Carbon monoxide is odorless and tasteless, meaning that a carbon monoxide detector may be the only way to know there's an issue. Carbon monoxide detectors come in several plug-in, battery-operated, and hardwired varieties. They even come in combination units, featuring both carbon monoxide and smoke detection from one device.

Combination models will give voice alerts to explain whether the issue is smoke or carbon monoxide-related.

Detector Location Best Practices
Always check with the AHJ, but there are some general rules and best practices when choosing detector locations:
Place smoke detectors in the bedrooms
Install a smoke and carbon monoxide detector just outside of the bedrooms in the hallway
Install a smoke and carbon monoxide on every level, including the basement, first floor, second floor, and attic

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From the makers of This Old House, America’s first and most trusted home improvement show, Ask This Old House answers the steady stream of home improvement questions asked by viewers across the United States. Covering topics from landscaping to electrical to HVAC and plumbing to painting and more. Ask This Old House features the experts from This Old House, including general contractor Tom Silva, plumbing and heating expert Richard Trethewey, landscape contractor Jenn Nawada, master carpenter Norm Abram, and host Kevin O’Connor. ASK This Old House helps you protect and preserve your greatest investment—your home.

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Understanding Smoke and Carbon Monoxide Detectors | Ask This Old House
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