This spring, we’ve seen living proof of the Chicago saying “If you don’t like the weather in Chicagoland, just wait five minutes” with temperatures dropping to freezing just 36 hours after temperatures hit a high of 80 degrees.
At Maertin Heating & Cooling, our customers frequently ask, “What do I do with my thermostat in the spring and autumn when we have these huge changes?” There is mass confusion about questions such as “Do you leave the fan in the “auto” position so the furnace and air will kick on at preset temperatures?” “Do you keep the fan set to the “On” position so air keeps circulating but without the heat or air conditioning?” “Is this causing wear and tear on my HVAC unit?”
We are here to explain. During spring and fall when temperatures are moderate, your heat or air conditioning may not be running very often, if at all. In buildings that are well sealed with closed windows, the indoor air can get stuffy from a lack of air circulation. Running your HVAC fan – setting it to “ON” and letting it run – can help keep freshen the air and help to dissipate odors.
Leaving your fan in the ON position
When your thermostat has the fan in the “on” position, the HVAC fan runs all the time, so more air is circulated through your HVAC filters and if you have them, air purification systems. This constant circulation can help to reduce airborne contaminants so less allergens like pollen and dust, VOCs, pollution, and even mold and bacteria that cause illness are in your home’s air.
However, the benefit you gain depends a great deal on the type of filter inside your HVAC system. Standard HVAC filters aren’t meant to trap particles as tiny as viruses, for example, or even some types of pollen. They are primarily meant to keep dust and debris out of your HVAC system. However, filters with a higher MERV rating can remove much smaller particles. When you have an air purification system installed in your HVAC ducts, you will see a greater benefit when keeping your HVAC fan running.
When your HVAC fan is always running, the effect is similar to running a ceiling fan. Air is moving and circulating constantly, so it will feel cooler in the summer and warmer in the winter. Your home’s temperature will be more equalized as air below is pulled above and recirculated.
Running a standard furnace fan constantly will increase your electric bill by $600 to $1200 a year and the fan will probably need to be replaced every 5 years or so. However, Maertin Heating and Cooling can install a new high efficiency ECM fan motor on any furnace, which would cut that increase to just $60 to $100 a year. We can also help you with a variable speed fan for even greater efficiency. This type of equipment has over 100 speeds, which flex faster or slower depending upon the cleanliness of your filter.
When you need to replace your furnace, it will include an ECM motor.
Leaving your fan in the “Off” or “Auto” position
You can opt to open windows for fresh air during pleasant weather, and if there is a breeze, Mother Nature will take care of air movement for you. Since your fan is not always running, you’ll be saving some money both in your utilities and fewer filters. However, when the fan is turning on and off, your equipment will incur more wear and tear.
| On Position | Auto Position |
| Even heating and cooling | No air circulation when off |
| Better air filtration | Less opportunity for air filtration |
| Uses more air filters | Air filters last longer |
| Slightly higher energy costs | Uses less energy |
| Fan lasts longer | Fan wears out faster |
Which Setting Is Best: On or Auto?
The choice really comes down to your personal preference. We here at Maertin Heating & Cooling recommend putting your fan in the ON position and leaving it there. If you prefer the AUTO setting, here is when you should consider switching your fan from “AUTO” to “ON.”
- You have allergy-sufferers. If you have people suffering from allergies in your home and it’s the height of springtime allergy season, leaving your fan in the “on” position will help filter pollen out of the air in your home. Make sure you’re equipping your HVAC returns with filters capable of trapping fine pollen and dust particles.
- It’s cleaning day. Cleaning will cause dust and pet dander to go airborne, so leave that fan on when you’re vacuuming, sweeping, and dusting to help pull those particles out of the air and into your HVAC filters.
- You have a full house. If you’re hosting a lot of guests, keeping the air circulating can help prevent your home from feeling overly stuffy.
- Cooling a hot (or cold) spot. If you’re using a part of the home that’s notably warmer or colder than other living areas in the home, keeping the fan running can help bring the temperature in that room in line with the rest of the house.
- Your HVAC is sitting dormant. During mild temperatures in the late spring and early fall you may go days or even weeks without turning on your heat or air. Turn on your fan to relieve stuffiness, reduce odors and make everyone more comfortable.
Still have questions about your fan setting, and what might be best for your family’s situation? Contact us by calling 708-479-9350 or clicking here to send an email. We will be happy to help keep you comfortable!