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Attic Ventilation Fans – Pros and Cons

Proper ventilation of a home’s attic can affect the overall temperature of the home, as well as affecting maintenance issues, such as the lifespan of roof shingles. There are several options available to deal with this problem, amongst which is an attic fan. The question is, is that attic fan worth it or is it just an unnecessary expense that isn’t going to provide much help?

Without proper ventilation, the attic space in a home can rise to as much as 150°F (65 °C) in the summer sun. Several factors will affect the actual temperature, including the ambient temperature and the color of the shingles on the home. Darker colored shingles will result in a higher internal temperature. 

Before going any farther, let me clarify one thing; there are two different types of fans that are installed in home attics, while they may seem similar or even like two names for the same thing, they are not. 

  • Attic ventilation fans draw hot air out of the attic, during the hottest times of the day, so as to keep that heat from pushing down into the rest of the home. They only pull air out of the attic. 
  • Whole house fans draw hot air up through the house during the cool of night, allowing cool air to come in through the downstairs windows, cooling the home. 

Of the two systems, an attic fan is the simpler, making it a better DIY project. The installation is limited to the attic itself, assuming that you have electric power run into your attic. If not, you may want to hire an electrician to run an electric line from the living area of your home or from the breaker box into the attic. 

The attic fan should always be installed with a thermostat, allowing the homeowner to set the temperature at which the fan operates. The lower the setting, the more the attic fan will help in keeping the home cool. However, there is a tradeoff here, as a lower temperature will cause the fan to run more, consuming more electricity and costing more to operate. 

Proper installation doesn’t just consist of the attic fan itself, but also of vents in the soffits of the home. These vents are there to draw replacement air in, to replace the air that is being drawn out of the attic space by the fan. If the vents are missing or have been painted over (a common problem), the attic fan will not work properly and may cause other problems. 

Pros to Installing an Attic Fan

Attic fans can be installed in homes in any climate, unlike whole house fans which are really only useful in a cool climate. How much benefit they will provide may vary, depending on the climate and any other attic ventilation that already exists. Obviously, the greatest gain would be in a home where there is not any proper ventilation before the attic fan is installed. 

Lower Temperatures in the Floor Below

By lowering the temperature in the attic, that heat isn’t available to radiate into the occupied floor of the home below. While heat rises, it can also radiate in all directions, including down. The ceiling of the top floor of a home will often be considerably warmer than the rest of the room, because of the higher temperature in the attic. This problem is even worse in older homes, where the attic insulation has packed down. 

Lowering the attic temperature will aid in lowering the overall temperature of the home, reducing the amount the air conditioning needs to run and the related energy costs. Less wear and tear on the HVAC system will help increase its life, saving on the expense of replacement. 

Longer Shingle Life

Most homes have asphalt shingles, with the asphalt layer covered in gravel. While solidified, the asphalt is still subject to heat. A hot attic can literally cook the shingles off your roof, causing the asphalt to soften and the gravel to fall off. This shortens the life of the roof, which should normally last 25 to 30 years. 

The most obvious sign of heat damage to the roof is fading. Other signs include curling of the shingles and blistering. The damaged roof will essentially look like it is old, long before its time.

Less Risk of Ice Damming

Ice damming happens to homes with poorly ventilated and insulated attics, in the wintertime. The warmth of the home’s heating system will raise the temperature in the attic above the ambient temperature outside, causing the roof to be warm enough to melt snow falling on it. However, the roof will not be uniformly warm. Due to the lesser volume of warm air beneath it, the roof near the eaves is cooler, allowing that water to re-freeze. This creates the dam. 

As further water flows down the roof, it encounters this dam, building it thicker. The thicker ice dam can cause water to pool and seep through the spaces between shingles, reaching the structural lumber below. This moisture is damaging to the home’s roof. 

Less Risk of Mold Buildup

Poorly ventilated attics are a prime place for mold and mildew to grow, damaging anything stored in the attic, as well as the wood structure supporting the roof. This is especially true in homes that suffer from ice damming. While this is not a prime reason for installing an attic fan, eliminating this risk is an added benefit of installing one. 

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Attic ventilation fan, Steve Rainwater

Cons to Installing an Attic Fan

While some pros are not in favor of attic fans, the pros outweigh the cons in most circumstances. The potential risks that these professionals are concerned about are easily overcome by insuring a proper installation of the fan. 

Roof Leaks

Improperly installed attic fans can cause leaks in the roof, allowing water to seep in and damage the sheathing and roof structure. Proper installation of the roof fan is essential, especially when it is installed in the roof itself, rather than a gable end. 

Increased Risk of Carbon Monoxide

If the aforementioned soffit vents are missing or plugged, either by paint or insulation, the attic fan can cause a lower atmospheric pressure in the attic, than exists in the rest of the home. That lower pressure will draw air up from the rest of the house, into the attic. Coupled with a gas-fired furnace for heating or a gas-fired hot water heater, this could cause exhaust gases from these appliances to be sucked into the living spaces of the home, rather than going up the chimney. 

Please note that this problem only exists when there is no provision for sufficient airflow to replenish the air being expelled from the attic by the attic fan. Normal operation of these appliances will not draw the carbon monoxide into your home, as long as there is adequate ventilation. 

Increased Energy Costs

Depending on the temperature that the attic fan is set to, the attic fan can actually use more energy than is being saved by the reduced use of your home’s air conditioning. This problem is even worse, in cases where there is inadequate attic ventilation, so the attic fan is actually drawing air conditioned air from your home into the attic and expelling it. Calculating the actual energy cost or savings is difficult, as each case is different. 

Conclusion

If your only reason to install an attic fan is to save money, you may be disappointed. The ROI on your investment may be much worse than you expect. Studies show that in some homes, recovery of the investment can take as long as 30 years. However, the other benefits mentioned above may make it worthwhile to install an attic fan in your home, even without this payback. 

If you live in a hot climate, where the air conditioning has trouble keeping up with cooling your home, an attic fan could make the difference, reducing the workload on the AC system and allowing it to keep your home cooler. 

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