September 21st, 2021

Cosmo here! Today The Boss told someone, “If your attic fan is fighting against your AC, you lose.” What does that mean???
If your AC seems to be working harder than it should be, it doesn’t necessarily mean that your Mercer County, NJ home needs AC repair. It could be that your attic fan is working against your AC. (This is one of the reasons we do not install or usually recommend attic fans). If you’re asking the question, “Do attic fans help?” the answer is: it depends.

Four Things to Know About Attic Fans and Vents

How do attic fans work?

Before discussing whether your attic fans are working for you or against you, you should understand how an attic fan works. When they work the way they’re supposed to, attic fans improve your air conditioner’s performance by removing hot air from your attic. The attic is generally the hottest part of the home because it’s not air conditioned and because the air is warmed by solar heat that the roof absorbs.

In a properly constructed modern home, the attic is a completely separate space from the living area of the home. Ideally, the heat in the attic will stay in the attic until it leaves the home. Natural convection draws fresh air in through the soffit vents and allows hot stale air out through the ridge vent. Attic fans aid this process by creating negative pressure and encouraging airflow through the attic. This brings in fresh air from outside and expels hot air out from the attic space. However, if your attic is not completely sealed and separate from your living space, the attic fan can suck cool conditioned air out of your home’s living space. 

How does an attic fan lead to cooling loss?

The scientific tenet that “nature abhors a vacuum” dates back to Aristotle, and still applies to building science. If the attic fan removes more air from the attic than is replaced through the soffit vent, the remainder of the replacement air has to come from somewhere, and that source is usually the living space. When this happens, conditioned air that you spent energy dollars to cool will be wasted. One way to minimize this is by checking your soffit vents. As notes, if your soffit vents are blocked and aren’t sufficiently sealed from the rest of the house, this helps create the conditions necessary for a negative pressure to occur.

Attic fan size matters…but does bigger mean better?

In the case of an attic fan, bigger is not necessarily better. One of the key things to remember about attic fans is that the amount of air being removed by the attic fan has to be replaced in equal measure by fresh air entering the attic through soffit or gable vents or someplace else. If the attic fan is too large, then that someplace else will be the conditioned space in the house. 

Will an attic fan thermostat help?

You don’t need to have your attic fun running all of the time. Having it running only when it’s needed maximizes its benefits for your home’s AC and overall energy efficiency. An attic fan thermostat can turn on the fan when it will be helpful and turn it off when it isn’t needed, adding to your savings and convenience.

As you can see, your roof and your HVAC system are closely linked. If any of these components of your roof or attic isn’t optimized for energy-efficiency, it can take a toll on your Princeton, NJ home’s HVAC system

What’s causing your HVAC system to be overworked: your roof/attic, your attic fans, a mechanical issue within the system itself, or something else? The best way to find out is with a diagnostic visit from SG Heating & Air Conditioning LLC. Whatever the problem is, we can identify it and discuss your options. For more information, call us at 609-448-1273 or fill out this form.

Now I know what The Boss meant when he was talking about AC systems and attic fans fighting against each other. I don’t want to fight anyone…but I bet I can beat you in a tug of war! Woof!!

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