Your Guide to Attic Fans

Attic ventilation is crucial to the overall quality and comfort of a home.

When an attic is ventilated properly, whether by natural ventilation or by power, it helps reduce cooling costs in the summer and protects the structural quality of the roof during heavy winters. An attic fan has many benefits, but it also has downsides, so you need to do your research before you purchase, install, and use these products.

attic fan

What is An Attic Fan?

Proper attic ventilation is important for many different reasons, and attic fans, also called powered attic ventilators, are machines designed to meet this need. Attic fans are ventilation units that regulate heat levels in a home or building’s attic, taking hot air from the interior of the attic and expelling it outward. While a manual switch is often used to turn the attic fans on and off, they can also be connected to an automatic switch that turns the unit off when certain internal temperatures are reached. This type of switch functions under the same principle as thermostats: when a specific temperature is reached, the switch is flipped.

Attic fans and attic ventilators are similar in function to regular box fans: they have a set number of fan blades (the number of fan blades can vary depending on the unit) housed inside a box that holds the fan in place. When the fan is on, the blades move air and create circulation in the attic space. Attic fans are installed in the roof or attic wall through a hole that needs to be pre-cut, forming a passage way for air to move from the interior of the attic to the outside.

The basic principle is that by moving air from the inside of the attic, which is hot, to the outside, the attic fan will increase home efficiency and enhance overall comfort. In theory, the cost and overall energy usage of electricity to run the fan will be less than the overall use and cost of operating the air conditioner.

As we’ll learn however, attic fans are not that simple...

Potential Benefit of Attic Fans

There are lots of theories for attic ventilators, and as you shop and search for products, you’ll discover there are many different ideas for the benefits of these systems.

While some claims hold more truth than others, and benefits often depend on the specific model and makeup of the house and attic, these are a few of the potential benefits for attic fans.

Ventilation

The biggest potential benefit for attic fans, in fact the main reason you would purchase one, is ventilation in the attic space. For attic fans, as opposed to whole house fans, we’re talking ventilation exclusively in the attic, and not in the general living space. Essentially, the goal is to create a slight attic breeze. Having ventilation in the attic can make a significant difference in many home-comfort factors, including cooling, air quality, and long-term structural quality.

Cooling

Because attic fans circulate air in the attic, removing warm air and replacing it with cooler air, the attic should stay cooler when the weather is hot. Regulating attic temperature is a significant advantage. As air sits in the attic, heat from the sun, which is transferred through the roof, warms the attic air. With an attic fan, this hot air is sent outside, while cooler air is pulled through vents near the rafters. This cooling effect not only helps the attic, it can in theory make the living space cooler because heat from the attic is expelled and not transferred to the lower levels.

Air Quality

Ventilation is an important part of improving indoor air quality. While you won’t spend much time in the attic, it still helps to have ventilation, which will remove dust, pollen, and other air contaminants that may pollute your space.

ice dams

Reduce Ice Dams

It’s not an obvious benefit for attic ventilators, but it’s an important one. Ice dams form when snow falls on your roof and begins to melt. The problem occurs at the eaves; because attic heat can’t reach it, the snow stays solid or forms into hard ice. Water from melted snow now trickles down and freezes on the cold eaves, creating a hard, solid dam. Ice then continues to accumulate, building a dam where melting water sits on your roof. The water can eventually seep under the shingles and into the house.

Ventilation from an attic fan, however, can help reduce the chances of ice dams by creating consistent melting across the entire roof. This benefit can be achieved through vents, but attic fans can help the air-movement process.

Side-Note: Preventing Ice Dams

If you have ice dams in the winter, there are many techniques you can use to remove the issue. Heated cables, for example, are laid near the gutters to heat the ice from the outside. They are fastened in a zig-zag pattern and attached with clips, but you’ll need to have them installed before foul weather sets in.

You can also rake the ice dams by pulling snow with special tools, reducing the amount of water that can pool near your roof’s edge. This is an ideal solution because it allows you to target specific spots while staying safely on the ground.

While these solutions are helpful, the most reliable way to reduce ice dams is proper ventilation in the attic. Always make sure your home has properly-ventilated eaves, ridges, and be sure to cap the hatch of the attic, which is the opening between the living space and the attic.

Prevent Mold

Another benefit of attic ventilators is mold prevention. Increasing air flow in an attic is a great way to reduce the chances of mold growth in a home. With the right amount of air movement, mold has a harder time getting the moisture it needs to thrive.

Ventilation can be used in the home, and, through the use of an attic fan, it can also help reduce the chances of mold in the attic.

These are just a few of the potential benefits that you could achieve by installing an attic fan.

But as we’ll learn, there are a few potential drawbacks for these systems as well.

Potential Downside of an Attic Fan

Like the benefits, there are many theories and differing points about the downsides of attic fans. Some experts, including Allison Barnes who writes for Energy Vanguard, recommend not installing attic fans.

Energy Inefficiency

Attic fans are meant to save energy and help the quality of the roof by preventing problems such as ice dams. However, they can create a burden on the air conditioner, causing the unit to work harder in order to keep the home comfortable.

The hope with attic fans is that they pull air from the outside, through vents near the edge of the roof, to create circulation and consistent attic temperature. The reality is that attic fans often pull air from the living space of the home, which has been run through the air conditioning, and not entirely from the outside.

This essentially means that the attic fan is pulling up pre-conditioned air (either cooled or heated), circulating it through the attic, and expelling it into the outside. Air that you are paying to cool is sucked up and tossed out because of the attic fan.

To keep the home cool, therefore, the air conditioning needs to work that much harder, resulting in a more expensive utility bill.

Negative Pressure

There is also a concern for negative pressure, which can lead to dangerous indoor air quality.

Let’s say you have a fireplace, for example, which uses gas to create a picturesque fire on cold winter evenings. Air contaminants, such as carbon dioxide, are expelled up through the vents into the outside, helping keep your indoor air safe.

However, if you have an attic fan, there can be inward suction, or negative pressure, pulling the harmful gases not outward, but into the home. You now have dangerous and potentially fatal gases leaking into the home.

Noise Issues

Another potential problem, although one that’s certainly not as serious, is noise from attic ventilators. Depending on the product you purchase, attic fans can create a slight hum or even a whine, especially as they age. An attic fan might be completely silent when it’s first installed, but through the years, it can start to make noise.

There are, fortunately, a few steps you can take to quiet a noisy attic fan...

Side Notes: Quieting a Loud Attic Fan

1. Tighten the Screws
In many cases, the noise is caused by loose screws that allow the fan to shift in place. Taking a screwdriver to the fan (when it’s off, of course!) and tightening the screws can often solve many of the noise issues.

2. Balance the Blades
If the problem is more of a clanking or clicking, as opposed to a hum or whine, the fan blades may be off balance. Many attic fans allow you to balance the blades, which can reduce the noise issues and also reduce internal pressure on the fan.

3. Replace the Ball Bearings
To create smooth cycling, most fans have small ball bearings that help lubricate the internal movement. Over time, these bearings will wear down and lose their ability to reduce friction. This can cause a lot of noise in the fan, but removing and replacing the bearings can fix the problem. You should be able to order new bearings from the manufacturer, although you may find them from the store where you originally purchased the attic fan.

Tips for Finding the Right Attic Fan

When you search for an attic fan, you’ll likely find two basic design styles.

The first is made for roof installation, while the second is intended for a gable wall.

Roof fans will be mounted on bases, which are made of either plastic or sheet metal. To install the roof-mounted fans, you’ll have to cut a hole near the peak and install the fan in the opening. Once in place, the fan is surrounded by shingles just like a typical roof vent or plumbing stack.

One of the most important considerations is size. You need to make sure you purchase a fan that is the right size for your attic and will move enough air to create the right amount of ventilation. The larger the attic, the larger and more powerful fan you will need.

In fact, if you have a significantly large home with a big attic, you may even need two attic fans to create enough ventilation.

Before you buy an attic ventilator, take the time to measure your attic and check the existing ventilation structure. The type and specific size will vary depending on your roof design and the location of your home, but in general you’ll need about one square foot of venting for every 300 square feet of attic floor space. If your attic has a tall ceiling, you may need more, and if your attic has a low ceiling, less ventilation space per square foot could be sufficient.

Another important factor is the climate in your area. If you live in a colder state, such as Minnesota or Michigan, you’ll have different needs for an attic fan than if you live in a warmer state, such as Florida or Texas.

If you live in a region that is warm all through the year, you are likely going to run the attic fan more often, which means you need a fan that has a long expected lifetime. Generally, the longer the expected lifespan, the more expensive the unit will be. However, if your region of the country is only hot for a few months in the summer, you can probably choose a unit that has a shorter lifespan and (generally) a lower price tag.

You should also consider the features that come with each fan. Some features are not necessary but make the fan more convenient, while other features may be required. Features that you may find in an attic fan include thermostat controls, insulation, screening, and motor sizes. There are even fans that can turn themselves off if extremely high temperatures, which could indicate a fire, are detected. This can prevent the attic breeze from stoking the flames of a house fire.

You should also consider the efficiency of an attic fan. Some will use more power than others, so if energy-use is a concern, search for a more efficient model or consider a solar-powered attic fan.

Regular vs Solar Attic Fans

While most attic fans use your home’s electrical system as the source for power, you can install units that use the power of the sun.

A solar attic fan has small solar panels, usually about the size of a dinner plate, that the fan uses to turn solar energy into fan-blade rotation. Once purchased and installed, solar attic fans operate at no cost, keeping your energy bills down, and because you won’t have to run wires, they are often cheaper to install. Of course, there are also eco-friendly benefits to reducing your electrical consumption.

However, solar fans will only function when there is strong sunlight, so if light is blocked, the fan’s rotation will be weaker, if it rotates at all. If your attic is still hot when the sun goes down, the fan becomes useless until sunrise.

There is also a power factor, as solar panels often rotate with less force than electrical models. Attic fans that are wired to the home’s system will give you consistent, powerful air movement, regardless of time, angle of the sun, cloud coverage, or shady obstructions, such as trees and neighboring houses.

construction project

Installing an Attic Fan

In many cases, the process of installing an attic fan may require the services of a trained and experienced professional. The project may involve cutting a hole in the roof, running electrical wires, properly sealing gaps, and lifting the fans, which aren’t extremely heavy but can be cumbersome and difficult to lift. In fact, having the fan installed for you is not a significantly-expensive project. According to HomeAdvisor, the average price for attic-fan installation is $560, and the high end is only $1,300.

Because of the difficulty and affordability, it may be best to use a professional. However, it is possible to complete the task yourself.

If you have a gable attic fan, as opposed to a roof-mounted attic fan, you will generally have an easier process. First you will have to install the shutters, then you will mount the fan in place. In most cases the fan will need a wooden box frame to hold the fan steady. When the gable attic fan is in place, you will need to run wiring to the location, so be extremely careful and make sure power is off before you move any wires. This is the part that probably most calls for a professional, as working with electrical wires can be complex, confusing, and dangerous.

If you are installing a roof-mounted attic fan, you’ll need to either replace the current vent or cut a hole in the roof for your new fan. You’ll need the right equipment and you’ll have to climb into the roof, so use extreme caution with this step.

The Importance of Rafter Vents

Insulation is an important aspect of sustainable home energy-efficiency. To keep the cool air in during the summer, and the warm air in during the winter, you have to seal the house and eliminate leaks. This means not only sealing the home, but also adding the right insulation. However, to have an attic fan that works properly, you have to have vents throughout that attic.

An air vent needs to be installed near the base of the rafters, allowing air to be sucked inward by the fan. With rafter vents, you are able to create air flow that starts at the base of the attic, pulling air directly from the outside. This can help keep the attic fan from pulling air from the living space, potentially reducing the chances of negative pressure and the inadvertent removal of conditioned air.

Rafter air vents help keep the soffits clear for air and create a channel for air movement from the outside into the attic. They are easy to install, and generally only require stapling onto the underside of the roof decking. When they are in place, you can install insulation up to the very edge of the attic. However, blown insulation may require additional blocking to prevent the insulation from blowing into the soffit. Usually a piece of board placed at the top of the rafter vent will do the trick.

The Difference Between Attic Fans and Whole House Fans

While the two can often be confused, there is a difference between attic fans and whole-house fans.

Attic fans are units intended to create ventilation strictly in the attic, but whole house fans, as the name suggests, are designed for ventilation in the entire home. A whole-house fan is an exhaust system that moves air from the home’s living space up into the attic while at the same time pulling in cooler air from the outside. Whereas attic fans are mounted to the roof or wall in the attic, whole house fans are generally installed in a gap between the living space and the attic.

Because whole-house fans are installed in the interior ceiling, they also require insulation when not in use. The better whole house fans come with an insulated damper box to solve this issue. If they are not insulated, warm air can seep through the gap, creating problems for your home efficiency. If you live in a cold climate, you’ll want to seal the whole-house fan to ensure comfortable temperatures in the winter.

The purpose of the whole house fan is to cool your home and in a much more energy efficient way than running the air conditioning system. Learn more about how an AC and whole house fan compare.

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