The Pro’s and Con’s of Continuously Running your Furnace Fan
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The Pro’s and Con’s of Continuously Running your Furnace Fan

Most thermostats provide an option that allows you to turn your furnace fan on, off, or to auto. Turning your furnace fan off essentially turns off your furnace. Turning the fan to auto means the fan will turn on when the furnace turns on. Lastly, turning your furnace fan to on means that the fan will continually run regardless of whether the furnace is generating heat.

But why would you want the fan on if the furnace wasn’t generating heat? There are a couple of good reasons to continuously run your fan. First, to address this issue, we need to understand what the fan does. When your fan is on, air is pulled through return vents, run through the ductwork to the furnace, and then pushed back out through the supply vents as heated air. Likewise, when your AC is on, air that is cooled by the AC is pushed through the supply vents via the fan. Clearly, the fan is an integral part of the system when trying to warm or cool your home. However, when the furnace or AC is off, how is it beneficial to run the fan?

Pro’s of setting the furnace fan to “On”

1. Great for allergy sufferers

If you have someone in the home who suffers from allergies, turning the furnace fan to on can provide them some well needed relief. This is especially true if you have a UV filter, or use the best filters for your system. The air in your home will be constantly filtered therefore improving the air quality of the home. However, if you do leave the furnace fan to on, you will need to change some filters more often.

2. Combats stack effect

If you live in a large home, or a multi-story home, setting the fan to on will help combat stack effect. Basically, stack effect acknowledges that hot air rises. Therefore, the upper levels of the home may be warmer than the lower levels. Running the furnace fan can help balance this out by continuously distributing the air throughout the home. Regardless of the size of your home, if you have some rooms that are hotter than others, running the furnace fan continuously may solve the issue.

3. Reduced humidity during the cold season

Running the fan during the cooling system helps to pull additional humidity from the air by continuously running the home’s air through the evaporator. Air that is less humid is more comfortable and may mean you do not need to set the air conditioner very low.

4. Lower electricity bill

This depends on your system. If your system is ENERGY STAR rated, then it was designed to run all the time. It is energy efficient and therefore shouldn’t raise your electricity bill very much. Also, many homeowners turn up their thermostats because one room is colder than another. Running the fan continuously balances out this issue, and therefore you may not need to have your heat set as high, or your air conditioning set as low—money saved!

5. May extend the life of your system

Again, ENERGY STAR rated equipment was designed to have the fan run continuously. Just like a car’s engine, starting and stopping is the hardest on the equipment. If your system was installed correctly then setting the fan to on will help extend the life of the equipment.

Cons of setting your furnace fan to “ON”

1. Higher electricity bill

If your equipment isn’t energy efficient it could raise your electric bill. Your air may be cleaner, but you will be paying for it.

2. Need to use your air conditioner more

If your house isn’t well insulated, or you have ductwork in the attic, then during the summer heated air from heated duct work or wall spaces will be sucked into the system and counteract the air conditioning. This means you will need to run your air conditioner more.

3. Need to change filter more

If your furnace filter is being used more then it will need to be change more often. Your air is cleaner, that is a good thing, but you need to spend more money on filters. If you have allergy sufferers in the house, it is probably worth the money.

4. Less energy efficient

Depending on your equipment, it may be less energy efficient but not by much. Again, this is one of those areas where you need to compare the comfort you are getting from having the fan continuously on, and the additional cost. Bottom line, leaving anything on is normally less efficient. The only exception would be if balancing the temperature in your home caused you to avoid setting more extreme temperatures on the thermostat.

Deciding whether to leave the furnace fan on really depends on your lifestyle and system. For example, if you work from home and suffer from indoor allergies, it may be well worth it for you to leave your furnace fan to on. If you work long hours outside the home, do not suffer from allergies, and have an older system, it would make sense to have the fan set to auto. Your HVAC expert should be able to help you identify the best setting for your home and needs.

With that said, when you are ready to upgrade your equipment make sure that it is ENERGY STAR rated, the right size for your home, has a variable fan option, and consider installing a smart thermostat that has more scheduling and customizable options. Lastly, if you are installing new equipment, make sure to ask that vent sealing is included as this can make a big difference in the efficiency and performance of your system.

If you are trying to decide whether to leave the furnace fan set to “ON” or “AUTO” give Robert B. Payne, Inc. a call. I am sure we can help you figure it out, and address any of your home comfort concerns.

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