One control on a thermostat that many people take for granted is the fan setting. Setting the thermostat fan control properly can make a big difference in home comfort and energy use. Learn the difference between the two fan settings and how one is usually better to use than the other.
First, it helps to understand the two main components of a forced-air heating and cooling system. The first is the equipment that actually heats or cools the air, and the second is the air handler or blower that circulates that conditioned air through your home via a network of ducts and registers or vents.
“On” and “Auto” Settings
Most thermostats have two fan settings: “auto” and “on” (or “fan only”). When the thermostat is set to “auto,” the fan only operates when the system is cooling or heating the air. When the air conditioner, furnace or heat pump cycles off, the fan goes off as well. When the thermostat is set to “on,” the fan stays on continuously, even when the system isn’t heating or cooling the air.
While some experts prefer the “on” setting, there are a few cons to consider.
- In homes with oversized A/Cs or heat pumps, setting your thermostat to “on” will handicap the dehumidification process. When the cooling system cycles off, some moisture will remain on the evaporator coil. The continued fan operation will blow across the coil and absorb that moisture back into the air. While the A/C is lowering the temperature, the air will still feel moist and clammy.
- Using the “on” setting 24/7 wastes energy.
- The constant hum of the air conditioner is an annoying sound to some when using the “on” setting. Additionally, running it constantly is expensive.
- If your ductwork leaks, running the fan continuously will result in greater loss of conditioned air, as well as more infiltration of dirty air into ducts.
For more helpful advice on setting your thermostat, please contact us at Marsh Heating & Air Conditioning. We proudly provide quality HVAC services to the Twin Cities area.
Our goal is to help educate our customers in Minneapolis-St. Paul, Minnesota about energy and home comfort issues (specific to HVAC systems). For more information about thermostats and other HVAC topics, download our free Home Comfort Resource guide.
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