Is running an HVAC blower fan continuously a good idea?
Yes it is, if your purpose is balanced temperatures and cleaner air.
However, running the blower all the time can produce unpleasant air temperatures from the grates between cycles. For example, cool air will be blown out of the air vents in winter when the furnace is not making warm air.
Those are common answers, and sometimes the debate among HVAC pros gets heated. Sites like Angi, The Family Handyman, Bob Villa and Forbes all give differing views.
The right answer is that running an HVAC fan all the time is a good idea in some circumstances, but isn’t a benefit in others.
This page discusses the pros and cons of running an HVAC fan continuously, when it makes sense and when you should set your thermostat to Auto mode. Newer thermostats have a mode called Circulate, and whether using that mode is a good idea is covered too.
*Tip: This page gives valuable information not found on most sites discussing this topic. It will assist you in making a decision that fits your specific needs, not a generic set of criteria, the climate and type of motor the blower is powered by.
Pros and Cons of Running a Blower Fan Continuously
Here are the general benefits and disadvantages of running the HVAC fan all the time.
The advantages of running the HVAC fan continuously are temperature balance, improved air quality and reduced energy use in peak warm and peak cold seasons.
- Temperatures get balanced and mixed. If one room is cool in winter during normal HVAC system operation, running the fan all the time will circulate warm air into that space, removing the chilly air. The reverse happens in summer when one room is too hot or too cold.
- The air won’t be stratified. This is similar to temperature balance. Stratification is when warm air rises and cool air sinks. This can make your feet cold in winter months. But when the blower runs a lot, even all the time, the air in the room gets mixed. It isn’t stratified to the same degree.
- Better air filtration = improved indoor air quality. When the fan runs continuously, the air goes through the filter more often, and the air gets a little cleaner each time.
- Energy savings are possible. How? Because the blower motor uses the most energy on startup – a lot more energy than when running. So, if it is in the ON mode instead of AUTO mode, the frequent starts that occur with Heat or AC cycles are eliminated. This is especially true during very cold weather and very hot weather when your HVAC system is going to run a lot of the time anyway. And it is also more pronounced with a newer ECM motor vs a PSC motor – explained in more detail below.
- The motor might be less stressed. Like any motor or engine, starting creates the most wear on it. Less starts = less wear and tear.
The cons of running your blower fan all the time are the filter getting dirty faster, the system working harder and reduced indoor climate control.
- You will have to change the filter more often – more air through it means the dust, hair and other guck will build up faster. But if you want cleaner air, isn’t that OK? The faster you filter out that stuff, the sooner you’ll be breathing easy.
- Dry and humid air gets mixed in during an AC cycle. The purpose of air conditioning is to remove humidity as well as heat. The moisture collects on the evaporator coil and drains away. The process continues for 5-15 minutes after the AC compressor stops and no additional heat is removed. If air continues to cycle before all the water is drained, the warm air will pick up some of that moisture and carry it back into your living space.
- Warm or cool air blowing on you. If the fan is running in winter when the furnace or heat pump is off, the air coming out of the grates will feel chilly (wind chill). The opposite will happen in summer – the air will feel warm and possibly humid.
- Higher energy use in off-peak seasons. During some seasons, the fan doesn’t normally run much. Turning the system to FAN ON mode will cause it to run non-stop and use energy it wouldn’t normally use during that season. For example, if your climate is warm and the furnace rarely runs in winter, FAN ON mode will raise energy use. The opposite is true for summers in cool climates.
- More stress on the blower – especially if the furnace filter is dense. For example, there is a significant air resistance difference between a MERV 8 filter, MERV 11 and MERV 13 filter. With high airflow resistance, the blower will work too hard and may fail.
Should an HVAC System Fan Run Continuously?
|In a Dry Climate||In a Humid Climate|
|The System Has an ECM Motor||The System Has a PSC Motor|
|You Prefer Better Air Filtering||You Prefer Lower Energy Cost|
|Reduce motor wear in peak seasons||Reduce motor wear in non-peak seasons|
|Priority is overall temperature balance||Priority is air temperature from grates|
The score so far: The pros and cons of running the blower all the time show the score to be 5 Cons and 5 Pros. That is why HVAC professionals argue about this topic.
But there is more to the story. Let’s make specific recommendations based on your climate and the type of blower motor in your air handler or furnace.
Climate Considerations and Running the HVAC Fan Continuously in Summer
Is your climate warm and humid? If yes, choose Auto mode. The reason is that dehumidification is a huge part of what your AC does – drying the air so that it is more comfortable. If the fan runs all the time, it will cycle warm air into the ductwork and over the drain where condensed humidity enters and leaves your home. Before all the water can drain, the warm air will evaporate some of the water and carry it back into your living space.
Auto Mode turns off the fan shortly after the AC compressor shuts off. With the fan off and no air circulating through the ductwork, the moisture that has been removed from the air in your living areas will drain away and be gone.
Is your climate dry – like in the Southwest and Rocky Mountain states? If yes, then running your HVAC fan continuously offers more benefits than problems. Letting excess humidity drain away isn’t a big issue – there’s very little of it to start with.
And when humidity isn’t a consideration, you can enjoy the benefits of running the HVAC system fan all the time – better temperature balance throughout your home plus cleaner air through ongoing air filtration.
*Reminder – If you are going to use FAN ON vs FAN AUTO most, remember to have an air filter with the right density – the right filter MERV, MPR or FPR rating, depending on the furnace filter brand.
Blower Fan Motor Considerations and FAN ON Mode
Your furnace or air handler has one of two kinds of blower motors.
A PSC motor is an older style and is still used in affordable HVAC systems. PSC stands for permanent split capacitor.
An ECM motor employs newer technology. They are used in most furnaces and air handlers now. ECM = Electronically commutated motor.
Studies reported by the US Office of Energy Efficiency & Renewable Energy on motors show that ECM motors average 33% higher efficiency than PSC motors. Another study shows that energy savings of 25% to 75% are realized with an ECM motor.n
PSC: Therefore, if your furnace or air handler has a PSC vs ECM motor, you might not want to run it continuously. You can always set the thermostat to AUTO mode and switch the fan to ON mode when you want to clear the air of cooking odors or run the air through the filter more consistently.
ECM: Your HVAC system won’t use a lot of extra energy running the fan continuously. Energy cost won’t be much higher – maybe $4-$8 more per month. If you want the benefits of continuous fan, then from an energy perspective, go for it.
Should the Fan on an HVAC System Continuously?
Yes – If you live in a dry climate and want improved air filtration and temperature balance, then running the HVAC fan all the time provides more advantages than disadvantages.
No – If your climate is humid, then your HVAC system will get rid of more humidity if you use AUTO mode.
Also, to prevent warm air in summer and cool air in winter coming from the grates, choose AUTO mode. This will ensure the fan shuts off between cycles.
What is a thermostat with Circulate Mode?
Honeywell T5 and T6, Emerson Sensi and other thermostat models offer thermostats with Circulate Mode. According to Honeywell, the Honeywell Circulate feature turns on the fan for 30% of the time every hour in order to circulate the air in your home. That’s 18 minutes per hour when the fan isn’t running for another reason.
Circulation mode gives you all the benefits of FAN ON mode – temperature balance, no heat stratification and better air quality. But it might also produce higher energy bills and cause the blower motor to wear out more quickly.
Is Fan On mode the same as circulating?
The terms are used interchangeably. But technically, there is a difference when comparing standard thermostats that can turn on the fan to run continuously and those with a circulation feature that runs the fan for a period of time each hour.