Smart thermostats are pretty popular these days because of all their conveniences. But one feature that’s less well known is that many of the new smart thermostats include a motion sensor setting. This setting lets the thermostat turn your home’s temperature down when you’re not home and back up when you and your family return. Pretty neat, right? Here’s more information about motion sensor thermostats and how they may save you money.
Motion sensor devices for heating and cooling have been around for about 20 years, primarily in spaces like hotels, dorms, military barracks, senior living facilities, and other multi-dwelling units. They were originally known as “occupancy-based thermostats,” and proved effective for energy management.
The same technology has been adapted for in-home thermostats. It relies on passive infrared (PIR) sensors, which measure infrared light radiating from objects in their fields of view — your basic motion detector.
These sensors are calibrated to be extremely sensitive, with the ability to distinguish between human and pet bodies, moving fan blades, and so on. Some are sensitive enough to detect body heat, even if you’re not moving — like when you’re sleeping.
The sensors transmit real-time data to the thermostat, which then raises or lowers the temperature based on the occupancy of the room. Sensors can be built right into thermostats, which can work well for zoned heating areas. For homes that aren’t zoned, individual PIR sensors can be installed throughout the home to keep temperatures consistent throughout.
Energy and Cost Savings
Motion sensor thermostats can save on energy bills, similarly to the savings from programmable thermostats, according to Keith Hill, resident HVAC expert. “These thermostats work like a programmable thermostat with a temperature setback, but by occupancy instead of the time of day. The effect on fuel savings would be similar,” Keith notes. "As a result, a lower setting (in heating mode) will save money when the space is unoccupied. And like a conventional programmable thermostat, the lower the setting and the longer the time in setback, the more you will save."
For those with highly variable or unpredictable schedules, a motion sensor thermostat may be even more efficient since it doesn’t rely on pre-set times and dates, which can also be a pain to keep updated. It’s possible a motion sensor thermostat could save even more than a programmable because heating and cooling are determined based on actual, not anticipated occupancy.
Things to Keep in Mind
No technology is perfect, and Keith points out that there may also be a few drawbacks to motion sensor thermostats. "If you’re setting back the temp because you like it cooler when you sleep and the thermostat is in the bedroom, then it will not set back because it will ‘see you’ and stay in occupied mode,” he says. Another possibility is that a large pet can trigger your temperature setting. Most sensors will ignore a small dog or most cats. But a larger dog, for example, could be interpreted as a human occupant. Conversely, if you want a pet to trigger your setting, that may not be possible, depending on their size.
One final caution Keith mentions is the time lag. “When you enter a cold room, the thermostat ‘sees’ you and calls for heat, but it may be 10 or 15 minutes before you feel comfortable — or even longer — depending on your setting,” he says.
As with most HVAC decisions, your personal and family needs, your home’s configuration and size, and your existing HVAC system are all factors to consider with any new technology. Luckily, your HVAC pro has all the up-to-date information and the technical knowledge to help you decide if motion sensors might be right for you.
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