Here is finally our ultimate guide on the pros and cons of powered attic fans.
There is a lot of information on attic fans, and we have distilled the best information in this article.
In this guide, you will learn that…
- Attic fans may protect your asphalt roof shingles
- Attic fans can lead to carbon monoxide poisoning
- Powered fans can dramatically lower the temperature of your attic
- Some professionals say attic fans do not lower energy usage, and may even raise it
- How attic fans can prevent ice damming
Let’s get into the details of the pros and cons of attic fans!
What Are Attic Ventilation Fans?
Powered attic fans are either installed on the roof or gable of a home.
They are intended to help reduce the temperature of the attic and to eliminate moisture buildup.
Attic fans are either powered by the home’s electrical system, solar powered, or wind powered.
The standard attic fan that is powered by the home’s electricity is controlled by a thermostat.
The thermostat is controllable by the homeowner, so the attic fan will turn on when the attic hits that temperature.
If the thermostat is set to 90 degrees Fahrenheit, when the attic reaches 90 degrees, the fan will turn on until the temperature drops below 90.
Solar powered attic fans use the energy from the sun to power the fan.
The solar panel will either be integrated with the fan, or there will be a separate solar panel that is attached by a cable to the fan.
Turbine fans are simply moved by wind energy.
Whole house fans primarily ventilate the interior of a home, but at the same time they ventilate the attic.
What Are The Pros?
The potential benefits of having an attic fan really depends on a few key factors such as…
- Your Climate. How hot does your attic get?
- Attic Insulation. Is your attic well insulated?
- Makeup Air. Does your attic have the proper amount of makeup or intake air?
- Air Sealing. Is your home properly air sealed from your attic?
1. How Does An Attic Fan Protect a Roof?
Probably one of the biggest and little known benefits of having good attic ventilation is that it can help prevent premature aging of your roof.
Many attics that I inspect just have old and degraded insulation, or missing insulation, and conditioned air leaks into the attic.
Also, there are usually issues with the passive ventilation system.
There are vents under the eaves called soffit venting which are commonly missing, inadequate, or even painted over.
The easiest sign for me that an asphalt shingle roof has prematurely aged is the color of the shingles.
As you can see in the picture below, this roof covering is actually only seven years old, but based on the fading, it appears to be more like a 20+ year roof!
Since standard roofing shingles are made from asphalt, which is derived from crude oil, when it heats up, it can literally “cook the shingles” on your roof.
The premature aging will show up in the faded coloring, as well as blistering and curling of the shingles.
According to Building Envelope Consultants, not only can a poorly ventilated attic accelerate shingle aging, it can even warp the wood sheathing of roof, leading to shingle bucking and ridging.
2. A Cooler House
Besides protecting a roof, lowering your attic temperature during warm weather will make your home overall more comfortable.
A hot attic will create temperature differences in the home, with the second level of a home being much warmer than downstairs.
During hot weather, the sun will heat up the roof, and this heat will transfer down to the attic through the wood framing and wood sheathing.
According to Oregon State University, the attic acts like a “heat trap” similar to how a car heats up when the windows are closed on a hot day.
And this extraordinary heat, sometimes up to 150 degrees, can still transfer heat to the home’s interior long after the sun has gone down.
In addition to helping cool down the home, a cooler attic may help reduce your air conditioning costs.
If you have a very hot attic, this heat will leak into the home, causing your air conditioner to work harder, and to run more often, which may dramatically increase your a/c costs.
Besides the increase energy usage, having your a/c run more often will prematurely age your air conditioner.
The average life expectancy for an air conditioner is about 15 years, but if it is run hard, it may only last 6-8 years.
3. Stop Mold Growth
A poorly ventilated attic can lead to mold growth, during cold or warm weather months.
During hot weather, you will have the a/c cranking out cold air in the home’s interior, and there will be hot air in the attic.
When these two different temperatures meet, condensation and moisture can form in the attic.
When there is darkness, moisture, and a food source (in the form of wood) mold growth can occur.
An attic vent fan can help reduce moisture in the attic, and thereby inhibit mold growth.
4. Eliminate Ice Damming
Ice damming is a strange phenomenon of a poorly ventilated attic, and it only happens during cold weather.
According to Attic Insulation Toronto, ice damming can have numerous causes and result in major issues.
Consider this: if the attic is poorly ventilated and insulated, the warm air can leak into the attic from the home’s interior, and this can cause snow to melt on the roof.
When this snow re-freezes, it turns to ice. And since the part of the roof closer to the eave is the coldest, the ice forms on the roof edge.
And when additional snow melts, it falls back down the roof to this mass of ice which now acts like a dam, holding back proper roof drainage.
This “dam” can cause water damage to the roof sheathing, and to the home’s wall — damage to wood joists, drywall etc.
This water intrusion into the home can also lead to mold growth.
What Are The Cons?
There are some potential negatives to installing an attic exhaust fan that homeowners should be aware of.
Some of these cons may just be benign annoyances such as increased noise, and others can literally be deadly.
Here are some well known possible disadvantages to attic fans…
1. Carbon Monoxide Risk
If you have natural gas (or propane) burning appliances such as a water heaters or furnace, then installing a powered attic fan can possibly be deadly.
(NOTE: This consideration doesn’t apply to solar powered or turbine attic fans because they are less powerful.)
According to the Home Improvement Contractors of Staten Island, the main reason that is happens is that powered attic fans can create a negative air pressure in the home’s interior.
When the home’s interior air becomes negative, it can literally pull the water heater (or furnace) combustion gases into the home, rather than venting to the exterior.
An easy way to find out if your home has a negative air pressure is to partially open a window when the attic exhaust fan is running.
If air is being pulled INTO the home, then it is under negative pressure.
However, this risk can be mitigated if you follow the manufacturer directions of the powered attic fan.
Attic fans are rated by CFM of cubic feet per minute, which is how much air the fan pulls in one minute.
The attic fans needs to have a minimum amount of “makeup air” or intake air which is the vent area that the attic fan pulls air from.
If there isn’t enough venting in the attic for the attic fan to pull air from, it will start “pulling air” from the home’s interior, through the wall cavities, and drywall ceilings.
As a home inspector, I always keeping at least one carbon monoxide alarm on each level.
2. May Increase Energy Costs
There have been studies performed that argue that attic fans do not decrease the energy usage of a home’s hvac system.
The authors stipulate that the energy required to run the attic vent fan offset any gains by increasing attic ventilation as a result of the fan.
In addition, the thermostatic attic fan may be pulling conditioned air from the home’s interior, thereby decreasing even further any energy gains as mentioned by the U.S. Energy Department.
Also, factoring the cost of the attic ventilation fan (and installation), it may take in excess of 30 years to regain the costs through increased energy efficiency because of increased attic ventilation.
3. Roof Leak Risk
Any time you install something onto a roof, there is a possibility of a roof leak.
The probably may be increased if improper flashing is used, or if the roof penetrations are not properly maintained.
Of course, a gable attic vent fan minimizes this risk because it isn’t installed on the roof.
According to FloridaDisaster.org, most attic fans (and other roof penetrations) are not designed to prevent water intrusion during hurricanes.
Attic fans are designed to keep out “normal” rainfall, but during hurricanes, the power of the wind can push water up the roof in sheets.
Are Attic Fans Worth It?
The problem with making a definitive statement on attic fans is that every house is different.
There are different climates all around the country, some climates are more beneficial to attic fans.
If you have good continuous soffit venting and a ridge vent, then any type of attic fan may be unnecessary.
The arguments against the energy efficiency of attic fans may be countered with the use of solar attic fans or even turbine attic fans.
Also, every house has different levels (and quality) of attic insulation and air sealing, which can dramatically affect the performance of attic fans.
In addition, many of the complaints from professionals about attic fans may be a result of improper installation such as inadequate venting for makeup air.
There a definitely positive testimonials from many users of attic fans around the country.
But there are also many negative sentiments from contractors and other professionals about attic fans.