After inspecting hundreds of properties as a home inspector, I have seen many different types of whole house fans and attic fans. A common question of my clients is the difference between the two, and that is why I wanted to create this guide.
Probably the biggest difference between whole house fans and attic fans is that a whole house fan is designed to cool the entire home by itself. A whole house fan is never used at the same time as an A/C system.
Attic fans are typically used together with A/C systems and they ventilate only the attic. Attic fans can only indirectly cool down your home by reducing the load on your central air conditioner and improving efficiency.
Whole House Fans Vs. Attic Fans: What's The Difference?
The main difference between whole house fans and attic fans is which part of the home is ventilated.
As the name implies, a whole house fan ventilates the entire home, while an attic fan ventilates only the attic.
Besides ventilation, a whole house fan is also meant to cool the entire home, and it is a type of natural cooling system that doesn't use refrigerant.
An attic fan can only indirectly help cool a home because a cooler attic reduces the load on the A/C system and improves efficiency.
What Is A Whole House Fan?
Whole house fans are powered fans that are typically 24-inches to 36-inches in diameter that will ventilate an entire house (including the attic).
Whole house fans are used to cool entire homes so owners don’t have to use the HVAC system. It can be up to 80%-90% cheaper to cool a home with a whole house fan rather than a standard air conditioner.
Many users also enjoy the breeze effect that a whole house fan can provide, and it gives a nice airy feeling to the home's interior.
- Cheaper to cool the home than using traditional HVAC systems.
- Gives a nice airy feeling on the inside known as the breeze effect.
- Whole house fans can cool down the home much quicker than a typical A/C.
- Whole house fans are significantly cheaper than A/C systems.
- They are sometimes used to get hot air out of the home right before the A/C is turned on.
- Some whole house fans (especially older and traditional types) are noisy.
- Work best only in cooler and drier climates. They don't work well in hot & humid areas of the country.
- Whole house fans are almost useless if it is very hot outside
- Whole house fans need at least 1-sf of attic venting per 750-cfm to work properly.
- Whole house fans are sources of air infiltration during winter. An insulated box should be placed over the unit when out of season.
Read Also >> How Does A Whole House Fan Work?
What Is An Attic Fan?
Attic fans are either installed on the roof or gable wall and used to ventilate only the attic. These specialized fans have thermostats so when the attic’s temperature reaches around 95ºF, it will automatically turn on.
Attic fans are mostly used to expel hot air during warm weather in order to cool down the attic and roof shingles. A cooler attic also helps the A/C system since less heat radiates downwards into the home.
Attic fans are also sometimes used during cold weather to help prevent ice damming, condensation, and mold growth.
- Helps the A/C system by cooling down the attic (less heat radiates into home)
- Ventilates the attic during cold weather to reduce moisture and mold growth
- Extends the life of asphalt shingles by reducing the roof temperature
- Can be easier to install than an entire soffit & ridge passive vent system
- Attic fans are a possible source of water intrusion.
- Attic fans need a minimum of 1-sf of intake openings for every 300-cfm.
- If the attic doesn't have adequate makeup air, conditioned air can be pulled from inside the home.
- Powered attic fans use electricity when in use but there are solar-powered models.
Read Also >> How Do Attic Fans Work?
Whole House Fan
How It Works
Ventilates the entire home by pulling in cooler outdoor air.
Ventilates only the attic and is installed on roof or gable wall.
Uses cooler outdoor air and skin evaporation for cooling effect.
Directly cools only the attic but can indirectly help the A/C system cool down entire home.
Usually by a wall switch or WiFi app.
Automatically with a thermostat but sometimes with wall switch.
$300 to $3,500
$100 to $600
How Do Whole House Fans Work For Cooling?
Whole house fans are only used when the outdoor air is cooler than inside of the home.
This is especially true when the sun goes down, and the outdoor temperature drops, but the home’s interior is still very warm.
Many people love whole house fans because when the sun goes down, they only have to run the whole house fan for 15-30 minutes and the home will be cool for the rest of the night. Whole house fans work best in drier climates and when there are large day to night temperature differences as reported by Kansas State University.
What Is The Whole House Fan Breeze Effect?
Some homeowners absolutely love the whole house fan breeze effect. This is when the whole house fan is used to give the interior a breezy feeling than just for the cooling.
It feels almost like having a low-speed desk fan on your skin, but it happens everywhere in the home.
Read Also >> What Are The Best Whole House Fans?
How Do Attic Fans Work For Cooling?
Attic fans can help a regular air conditioner in cooling down the home. During warm weather, if the attic gets hot, then heat will radiate from the attic and into the home (especially the top level).
This just makes it that much harder for your air conditioner to cool down the home. The A/C will use more energy, will turn on more frequent, and it will make your home less comfortable.
In my experience as a home inspector, the most uncomfortable homes are those with large temperature differences such as a hot upper level. These homes usually have a poorly ventilated attic.
How Do Attic Fans Prevent Ice Damming?
During the cold season, if warm air enters your attic from the homes interior, excessive heat can lead to a phenomenon known as ice damming that can cause severe damage to a home. Basically, your attic gets too hot when it's cold outside, and it melts snow on the roof.
When this melted snow gets close to the roofs edge, it refreezes, and creates a quasi ice dam. This ice dam holds back more water, and can lead to water infiltration and roof damage.
Read Also >> How To Install An Attic Fan On The Roof?
Do Attic Fans Prevent Mold Growth?
Too much attic moisture can also lead to hazardous and costly mold growth. Moisture primarily occurs when two air masses meet at different temperatures. For example, if the attic is cold, but the home's interior is hot—or when the attic is hot but the home is cold.
When these two air temperatures meet in the attic, it can cause moisture to form on the roof sheathing, framing, and paper-faced insulation.
And mold only needs three things to grow; a food source, moisture, and darkness. If excess moisture is formed in the attic, then mold has everything it needs to take root.
Can Attic Fans Protect Asphalt Shingles?
A commonly overlooked benefit of attic fans is that they can help protect and prolong asphalt roof shingles. Asphalt shingles will prematurely age if they get excessively hot.
When the attic gets very hot, the suns rays quickly heat up the shingles, and this heat transfers to the roof sheathing and wood rafters. This heat transfers to the attic air and becomes a type of heat trap just like how your car heats up with the windows rolled up when parked.
Read Also >> How To Use Whole House Fans With 2-Story Home?
How Are Whole House Fans And Attic Fans Controlled?
Whole house fans are turned on manually by homeowners through a wall switch (or phone app) because 2-3 windows need to be open for it to work.
We don't recommend using a thermostat or any type of scheduled activation of whole house fans.
If a whole house fan is turned on when a few windows (or doors) aren't open, it will cause air pressure problems in the home such as backdrafting as explained by the U.S. Department of Energy.
Attic fans in contrast are almost always controlled with thermostats that turn them on when the temperature outside reaches 95ºF. However, attic fans can also be turned on manually with a wall switch or even a phone app as well.
What Are The Risks of Whole House Fans And Attic Fans?
There are a few risks when homeowners decide to install whole house fans and attic fans.
- Sucking Air From The Home Interior
An important part of installing whole house fans and attic fans is having adequate venting or makeup air in the attic explained at EnergyStar.gov. If there isn't enough open venting in the attic, then when you use a whole house fan or attic fan—it will suck in conditioned air from the interior of the home. This would increase the costs of the A/C system.
Before installing one of these appliances, homeowners should verify that there is enough venting and also that the current soffit, ridge, or gable vents aren't blocked by debris or insulation.
It is also important to have a well-insulated attic with over 10-inches of insulation as well as air sealing all recessed lights, bathroom fans, and other ceiling penetrations.
- Carbon Monoxide Hazards
If you install an overly powerful attic fan or whole house fan, and if you have gas-combustion appliances, it may cause a dangerous situation of backdrafting.
Backdrafting occurs when gas byproducts are sucked into the home rather than going outside. Whole house fans should never be operated if you have gas appliances such as a dryer or water heater.
- Declining Use
Very few new and modern homes are built with whole house fans or attic fans.
Most home professionals (including home inspectors) don't recommend these appliances since a properly insulated, air-sealed, and ventilated attic won't have a need for powered attic fans or whole house fans.
But if you have an older home and it's in the right climate, a whole house fan or attic fan may work great for your home.
- Air And Water Leaks
Attic fans are frequently a source of water intrusion. Basically, any type of hole in the roof may be a water leak risk such as attic fans, skylights, plumbing vents etc.
Whole house fans are also a source of interior air leakage during winter. Since hot air rises, the whole house fan is basically like having an open window in the home during cold weather. Whole house fans need to have an insulated box installed over them during the winter.
Some whole house fans have insulated dampers that automatically close when not in use.
- Attic Fans Creating Venting Conflicts
Sometimes if attic fans are installed too close to each other (or passive vents), it can create ventilation conflicts and subsequent hot spots.
If two attic fans are installed close to each other, one attic fan will pull air from the other attic fan, disrupting any ventilation gains.
Or if an attic fan is installed close to a ridge vent, it will pull in air from the ridge while disrupting airflow from the eaves or soffits—leading to hot spots at the bottom of the attic.
- Vermiculite Or Other Toxic Substances Can Be Pulled Into Home
Vermiculite is a type of asbestos-containing insulation that is no longer used in the U.S., but some homes still have it.
If the whole house fan or attic fan causes attic air to be pushed back into the home interior, it can result in asbestos or other toxins going into the house.
Read Also >> What Are The Best Gable Attic Fans?
Where Do Whole House Fans And Attic Fans Work Best?
Whole house fans and attic fans work best in certain climates and areas of the country.
Whole house fans work best in drier and cooler climates.
Attic fans work best for cooling in hot climates and work best to reduce moisture and mold growth in cold climates.
What Is Better An Attic Fan Or Whole House Fan?
It is impossible to say whether a whole house fan or an attic fan is better because they have different purposes.
An attic fan is designed to turn on during the hottest part of the day to keep the attic cool and indirectly help the home's HVAC system.
A whole house fan is designed to be used primarily in the morning and early evening when the outdoor air is cooler. Whole house fans are used to totally replace a traditional air conditioning system when conditions are right.
What Are The Negatives Of A Whole House Fan?
The negatives of whole house fans are that they only work when the outdoor temperature is cooler than the interior temperature.
Whole house fans are also sometimes noisy (depending on model) and can become a source of air leakage if they aren't insulated and covered during winter.
Read Also >> What Are The Pros And Cons of Attic Fans?
Are Attic Fans and Whole House Fans The Same Thing?
Even though whole house fans are sometimes called attic fans, they are completely separate appliances with different functions.
Attic fans are installed on the roof or gable wall and are designed to ventilate just the attic.
Whole house fans are installed on the ceiling of the highest home level and ventilate the entire home.
What Are The Different Types of Whole House Fans And Attic Fans?
The two main types of whole house fans are ducted whole house fans and ductless whole house fans.
Ducted whole house fans have a duct that runs from the appliance to the outside which helps reduce noise and increases efficiency.
And the two main types of attic fans are gable attic fans and roof-mounted attic fans. Solar powered attic fans are also popular in the south where there is a lot of sunshine.
Final Thoughts On Whole House Fans Vs. Attic Fans
Whole house fans are sometimes called 'attic fans' but they are in reality separate appliances.
Attic fans turn on during the hottest part of the day, and may be running at the same time as your A/C system. Attic fans are sometimes used during winter to reduce moisture and to stop ice damming.
Whole house fans are only turned on when the exterior is cooler than the interior which usually happens in the early morning or early evening. Whole house fans are used to ventilate and cool the entire home so you don't have to use the A/C system at all.
Please drop a question or comment below if you have any stories or tips for whole house fans and attic fans! Thank you for reading our guide.