In direct sunlight. If the sun is shining through a window directly on your thermostat, your thermostat will think your home is hotter than it actually is. This will cause your air conditioner to operate more often than it needs to, which will make your home too cool and cause your system to consume more energy.
Near air vents. If your thermostat is near an air vent, cool air from your air conditioner can blow on it and your thermostat will think it’s cooler than it really is. This can cause your air conditioner to short-cycle, which is bad for your system and your home comfort.
Near other drafts. In addition to your air vents, drafts can come from windows, doors, fans and other places that can influence your thermostat’s temperature readings.
Near heat-producing appliances. If your thermostat is near any heat-producing appliances (especially near your kitchen), your thermostat will get warmer readings than the rest of your home and tell your air conditioner to stay on longer.
In a de-centralized location. Your thermostat should be placed in the center of your home, because that’s where you’re most likely to get an average reading of your home’s temperature levels. If it’s not in a central location, its temperature readings will likely not reflect the rest of your house and your home will either be too hot or too cold.