July 12, 2020

Most people keep their thermostat set to “Auto” all day, every day, without even thinking about it. However, you may see the “On” setting and wonder, “should I be using that instead?” After all, they wouldn’t put it there if it wasn’t meant to be used.

But turning your thermostat to “On” could be a mistake. Here’s why.

What Are the Differences Between ‘Auto’ and ‘On’?

When your thermostat is turned to “Auto,” the fan that blows the warmed or cooled air through your ducts only turns on when your furnace or air conditioner is running. This way, the fan is blowing conditioned air only when it is on.

On the other hand, with the “On” setting, your fan is always on, constantly blowing air whether that air has been conditioned or not. It also means that your air returns are constantly taking air in — air that’s already at the set temperature — and taking it back to the fan just to be blown back into the house. This isn’t a always good idea for a few reasons.

Excessive Wear on Your Fan

Your blower fan is one of the most taxed parts of your heating and cooling system already. It works any time your system is on, whether it’s heating or cooling. For this reason, it can also be one of the most likely parts of the system to break down.

Your blower fan doesn’t need more work, but by setting your thermostat to “On,” that’s exactly what it’s getting. Instead of cycling on and off with the rest of the system, using the “On” setting means that the fan never gets a break, which can lead it to break down earlier than it otherwise would.

Uses More Energy

While your blower fan doesn’t use as much energy as your air conditioner’s compressor, it still uses quite a bit. The energy from running it constantly can add up over time, leading to a shock when you get this month’s power bill.

While you may think that having the fan always blowing would mean that your air conditioner would have to work less, leading to a reduction in power usage, this isn’t the case. Instead, the fan is actively taking pleasant air out of your rooms and recirculating that same air. And on the way, some of that air is lost: about 10% of the air that is cycled through your ducts is lost through gaps in those ducts. So by constantly running the fan, you are effectively losing cool air through your ducts, without any cool air to replace it.

Makes the Air More Humid

When your air conditioner is on, the coil acts as a dehumidifier for your house, because water from the air condenses on it as the air is pushed past the coil. But with the coil off, any air moving through the system is not being dehumidified. Worse, any water left on the coil is being blown back into the air, making the house more humid than it would be otherwise.

Turning your thermostat to “On” during the summer can raise the relative humidity in your house by 10 to 15%, which can be both uncomfortable and unhealthy. If controlling your home’s humidity is already a problem, using the “On” setting will only make it worse.

Keeping your thermostat on the “On” setting does have one health benefit: it will run more air through your system’s filter. This allows the system to filter out more dust and other particles from the air. But this benefit can only be fully realized if you change your system’s filter regularly. Naturally, it will also mean that you must change your filter more often. Unfortunately, this isn’t the most efficient way to filter your home’s air. If air cleanliness is a concern for you, consider adding an air purifier to your system.

If you have any more questions about your thermostat, or if you’re interested in upgrading to a new smart thermostat, contact WK Mechanical, Inc. in Middletown, NY, today. We have trained and certified technicians who can handle any problem with your furnace or air conditioner. Our crew excels at repair and maintenance jobs. We also install new furnaces, air conditioners, boilers and products to improve your indoor air quality or water quality. Call us today to schedule an appointment.

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