Should I Set My Furnace Fan to ‘On’ or ‘Auto’ in the Winter? Ask an HVAC Expert

Our friend Pat in Sacramento has a question for us today about how best to operate his thermostat during the winter. Pat says:

“Hey there, Bell Brothers team! My name is Pat and I live in Sacramento. As you mention all the time, in our area we have fairly cold and wet winters. So, I don’t think it should really come as a surprise when I tell you that during those winters I find myself running my furnace pretty often. I also know that you like to talk about energy efficiency a lot, which brings me to my question.

I’m a normal red-blooded homeowner, and I want to be as energy efficient as possible with my heating because it saves me money on my utility bills and also it’s the right thing to do for the planet. With that in mind, my question is about my thermostat. Should I set my furnace fan to ‘on’ or to ‘auto’ in the winter? Asking an expert seemed like the route to go here because I’ve definitely heard conflicting things from friends in neighbors in the past. Thanks in advance for your great answer!” – Pat from Sacramento

You are a smart man, Pat, for deciding to ignore the conflicting advice and come straight to a heating expert. Hats off to you for that one, and hey, guess what? You’re far from alone with your inquiry. This question of whether you should set the furnace fan to “on” or “auto” in the winters is an ask an expert question we get a lot. Now, it’s our pleasure today to give you your answer!

Should I Set My Furnace Fan to “On” or “Auto” in Winter?

Let’s get right down to the basics. “On” means that your furnace fan will be continuously running, while “auto” means that it will run in order to match the temperature in your house to what you’ve set your thermostat to. The truth is, it varies which is the better choice for you. Personally, I prefer “auto,” but let’s take a look at the pros and cons of each now:

• Pros for “On”: When the furnace fan is set to “on,” air is being cycled through your HVAC’s filtration system continuously. This means better air quality—provided you change your filter every few months. Keeping the fan running also leads to even air distribution through your home. Stops and starts can be rigorous for your HVAC too, so this might prolong its life.
• Cons for “On”: Simply put, leaving your fan on raises your costs and burns more energy. You also have to replace your air filter more frequently since more air cycles through it. And, in the winter, it can chill you out since your fan will keep running even when the furnace is not producing heat. This means that, at times, it will circulate cold air.
• Pros for “Auto”: If you set your furnace fan to “auto,” the fan will only run when the system tells it to in order to keep your home as warm as you want it based on your thermostat settings. This means it’s consuming less energy than when it runs non-stop, which means lower furnace bills. Your air filters will also last longer this way.
• Cons for “Auto”: When your system stops and starts more, it means more wear and tear on your furnace, much the same as it does on your AC (which we explained when we discussed what temperature to set an AC to in summer). Your heating might also feel less even this way, especially when the furnace isn’t running or first kicks on (although an HVAC professional can fix this by improving your insulation and balancing your ducts and vents).

Why It Matters If You Set Your Furnace Fan to “On” or “Auto”

As we noted above, this matters for a few different reasons. The option you choose has an impact on how much money you end up spending, how much power your HVAC system burns during the winter, how often you have to change your air filter, and more. It can also affect whether or not your home is heated evenly.

In my opinion, though, the biggest and most important factors are the money and the energy efficiency. That’s why I noted that for me personally, I use the “auto” setting. The truth is that the concerns about wear and tear are pretty minimal if you have an HVAC pro out each fall and spring to check your furnace and AC respectively. Energy efficiency, which we’ll talk more about in the next section, is a far bigger concern.

Energy Efficient Heating Advice for How to Set Your Furnace Fan in Winter

When it comes to whether you should set your furnace fan to “on” or to “auto” in winter, the answer for me is “auto” because it’s the move that has the most to do with energy efficiency. It is not, however, the only thing you can do this winter to bolster your HVAC system’s energy efficiency. For example, I highly recommend looking into the benefits of installing a smart thermostat as well.

I highly recommend looking into the benefits of installing a smart thermostat as well.

There are, of course, other easy ways to make your home energy efficient, but for my money, investing in a smart thermostat is definitely one of the best. With a smart thermostat, you can actually program your furnace to turn on exactly when and for how long you want it to. This guarantees your house can always be as warm as you’d like, while minimizing how much your system stops and starts in order to cut down on wear and tear. I highly recommend it.

It’s a great question that Pat had, one we hear somewhat frequently. While the answer is that there are pros and cons to both, I personally recommend using the “auto” function over the “on” function for your furnace fan. The amount of money you save and the boost in energy efficiency is the reason why.

I also suggest having a smart thermostat installed in your home. Here at Bell Brothers, you can call us out to come give you an estimate for a smart thermostat. We can tell you whether your home is a good fit, and we can also help you come up with other ways to make your home more energy efficient. So give us a call today!

Contact the HVAC professionals at Bell Brothers to schedule an appointment to have the energy efficiency or your home, and your heating and cooling systems looked at today. We’ll offer recommendations and upgrades that are sure to increase your year-round comfort—and decrease your power bills. Contact our team today.

Wondering how to finance a new HVAC system, windows, or plumbing? HERO is a unique financing option that helps California homeowners afford energy efficient upgrades to their home. Contact Bell Brothers, a HERO-approved contractor, to learn more. Our local HVAC, plumbing, and window specialists will walk you through the entire process, from applications to installation.

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