HVAC Fan Settings and Speeds

Ceiling fan

The central heating and air conditioning systems of most American homes look very similar when it comes down to it. There’s variety in brands and models, sizes, and types, but all in all, there are some basic components that make up most of these HVAC systems. The most common HVAC system includes a furnace and an air conditioner, which is itself made up of an indoor unit and an outdoor unit. Then ductwork connects these machines to the rest of the house. The blower fan is the source of delivery. It’s an essential part of this operation that allows the cooled or heated air to be blown throughout the house.

Air conditioning in Austin is an essential part of life. And the blower fan lies at the center of this operation. It being such an essential part of this process, the kind of blower fan you have and the settings you use have a great impact on the air in your home. In this tip of the day, we’ll look at the different settings your central HVAC fan has and what differences come about due to those settings. We’ll also look at a newer kind of blower fan technology called variable-speed fans and what kind of benefits this kind of upgrade can have to your comfort and energy efficiency.

Two Fan Settings

There aren’t a lot of things about your air conditioner and heater you can directly control with your thermostat despite the fact that it is the interface between yourself and your HVAC system. Thermostats are purposely designed to be as straightforward and utilitarian as possible. Even still, many people don’t fully understand what the different settings their thermostat has done.

Essentially, most thermostats give you control of four things, whether or not your HVAC system as a whole is on or off, whether it’s going to turn the heater or the air conditioner on when it runs, what temperature you want the air in your home to reach with the help of the air conditioner or heater, and finally, what the focus of this tip of the day is, the fan setting.

Your fan has two settings you can control from the thermostat. One is “on” and the other is “auto.” They might be labeled slightly differently depending on your system and your thermostat but the differences between the two settings are standard. Almost every thermostat features separate controls for your Austin heating and air conditioning system and fan control.

To simplify things further, for purposes of this discussion, your air conditioner has two components: the part that cools and the part that moves the air. You adjust the part the cools by changing the temperature setting on your thermostat. You can affect the air movement by setting the fan to auto or on. When the fan is in auto mode, the air conditioner moves air only when the cooling part is running. When the thermostat senses that the house has reached the setpoint, it shuts off both the cooling and the fan. When the fan's in the on mode, the fan keeps running continuously, even when the cooling part is turned off.

That’s it. That’s the difference in a nutshell, whether or not the fan runs continuously or runs only when the heater or air conditioner is active and trying to change your home’s temperature. It seems like a small thing but the difference can have a significant impact on your home’s air quality, comfort levels, and energy efficiency. Let’s look at some of those consequences.

Pros and Cons of the “Auto” Setting

First, a brief overview of the “auto” setting to keep it straight in the head: The fan only runs when the furnace tells it to. During heating, the fan is controlled by either a timer circuit or a limit circuit in the unit. The fan will start about 40 seconds after the burner's light and go off about one minute after the temperature is satisfied. On cooling, the fan will run only when the air conditioner is running. The fact that the settings are so similarly named, not something as obvious as “off” and “on” makes it difficult for some people to intuitively understand the difference between the two, hence the elaboration.

So the “auto” setting makes the fan change automatically in conjunction with the turning on and off of the heater or air conditioner. What are the benefits of leaving your thermostat set in this position? The "auto" setting means less energy usage because it keeps the fan running the least amount of time at the slowest speed needed for heating and cooling. Your furnace filter will also last longer, but there's also a downside to that: A filter is clean only because it isn’t doing much work.

So that’s the main pro to the “auto” settings, it is by far the best setting for your energy bill. The primary benefit to using the “auto setting is to cut back on energy consumption, and in turn reduce your utility bills because by giving the fan a break between cooling cycles, you're also reducing wear and tear, allowing you to go longer periods between preventative maintenance. The average air conditioner has a 500-watt fan, which can use about as much energy over the course of a year as a refrigerator. The costs of running it 24/7 quickly add up.

You may be thinking though, if that’s so, what cons could be using the “auto” setting cause? Well, those lie mostly in the realm of comfort and circulation. The biggest air quality downside to the “auto” setting is that your household air will gradually grow stagnant between cooling cycles. If you don’t open the windows during the mild seasons, things could get pretty stuffy before the air conditioner kicks on again. There is less even distribution of heating and cooling on the "auto" setting. Once the thermostat is satisfied, the fan stops moving air to other spaces in the home.

In addition, there’s something to be said about wear and tear and starting and stopping. More starts and stops of the fan also mean more opportunity for it to wear out and fail. So especially in cases when your air conditioner is turning on and off frequently, such as if you have an oversized AC or heater, the fan is going to be starting up again frequently which could lead to it needing repairs more frequently.

Pros and Cons of the “On” Setting

Most people keep their fans in the “auto” position. It’s a position that makes a lot of sense for most situations and most people’s preferences. That being said, there wouldn’t be an option to switch to “on” mode if it didn’t have its advantages as well. There are a time and a place for the “on” setting just as there is for the “auto” setting.

As far as leaving the system in the “on” position by default, the biggest benefit you’ll see is in circulation. It makes sense intuitively that if the fan is on all the time the air is going to circulate more and stagnation will be eliminated. Air is being replaced continuously, so your indoor air will seem fresher and household odors will be less noticeable. Allergy sufferers may especially benefit from this endless circulation.

Another potential downside of using the “on” setting is that it can draw humid outdoor air into your home between cooling cycles. If you live in an arid region, this is unlikely to be a concern. But in humid environments, like ours in Austin, especially during the summer, you might want to counteract this effect with whole-home dehumidification if you need a continuous fan to improve indoor air quality.

So essentially the “on” and “auto” settings are going to have opposite pros. The pro-con balance is flipped when you switch to the “on” setting. With the fan blowing continuously, your indoor air is always being filtered and replaced. While this treated air is more pleasant for everyone to breathe, it's especially important to people with sensitive allergies or respiratory conditions.

That leads to the biggest downside, the energy usage. Using any appliance more often means more energy usage which means bigger utility bills. The same is true with the fan in your HVAC system. That’s why if you keep your fan in the “on” setting, you'll likely see a difference in your utility bills, and you'll want to be a little more proactive about routine maintenance to your HVAC system. You'll also need to be diligent about replacing the air filter, which will clog up faster than it would under the “auto” setting because more air is going through it and carrying things with it.

Leaving your fan in the “on” setting can be particularly problematic if your air conditioner is oversized, which is, unfortunately, more likely than you’d think. Since your AC is responsible for doing two jobs, cooling and dehumidifying, moisture from the air condenses on the cold evaporator coil when it runs. An oversized AC will shut off after a short run time and leave a lot of water sitting on the coil. By running the fan after the coil warms up, a lot of that water will evaporate and be put right back into your home.

So, putting the fan in the on position compounds the error of having an oversized cooling system. Your house will cool down quickly without dehumidifying well. Running the fan continuously makes the dehumidification worse and your home less comfortable.

Variable Speed Fans

There is actually a middle ground between the “on” and “auto” setting, but not so with any average HVAC system. If you find that you like the benefits of the “on” setting but wish you could reduce the additional operating cost, that’s something to consider when your air conditioner nears the end of its life. Some models are available with variable speed fans that offer greater customization of airflow during cooling cycles and in-between. You can program these units for high fan speeds while the A/C is on and slower speeds when the system is just circulating the air.

A variable-speed fan combines both the benefits of the “on” setting and the “auto” setting. For one thing, variable speed fans allow you to combine high indoor air quality with energy efficiency. When the AC isn't actively cooling, the fan slows down, saving electricity. But rather than shutting off altogether, the fan keeps blowing so the air is still being circulated and filtered at all times. This can be a lifesaver for people who suffer from allergies or other respiratory ailments.

The constant fan action also helps keep the air temperature consistent throughout the home, so certain areas don't end up hotter or cooler than others. Furthermore, the noise level is lower than leaving the fan on full blast all the time, so your home ambiance will be a little more amenable for relaxation. But of course, because the fan now has different speeds, it doesn’t have to suck as much energy to run during the periods between cycles of air conditioner on times, so it won’t make as much of an impact on your filter or energy usage.

Fan Speeds and Air Conditioning Repair in Austin

The settings on your thermostat are now less of a mystery. We’ve uncovered some of the arguments for the “auto” setting and the “on” setting and the upgrade that acts as a compromise between the two. But don’t forget that regardless of your fan’s setting, proactive maintenance is a necessity if you want your HVAC system to last as long as possible.

AC Express is the place to call for AC repair in Austin. We are an Austin AC repair company that operates all throughout the Travis County area and beyond, from Cedar Park and Georgetown to Lago Vista and Lakeway. If you need AC or heater repair in Austin don’t hesitate, call today!