People often mistake whole house fans for attic fans. Many think that they are the same, but people couldn’t be more wrong. Even though the appearance of both types of fans is very similar, they have very different functions. So what are the differences between an attic fan and a whole house fan? How can you tell them apart?
An attic fan is used to remove hot air from the attic to the outside whereas a whole house fan is used to move cool air from outside the house into the living areas. An attic fan is used to lower the attic temperature while a whole house fan is used to lower the temperature inside the living spaces.
Both types of fans work to lower the temperature of the house. But attic fans are used when it is hotter outside and whole house fans are used when it is colder outside.
There are many other interesting differences between an attic and a whole house fan, here are they;
| Attic fan | Whole house fan |
|---|---|
| Removes hot air from the attic to the outside | Brings cool air from the outside to living areas while removing the hot air into the attic |
| Smaller in size and power compared to whole house fans | Larger in size and power rating |
| Easy installation | Installation is not as easy as that of attic fans |
| Installed on the roof or gable | Installed on the ceiling |
| Quieter operation since it is installed away from the ceiling | Usually noisy if installed on the ceiling |
| Costs less | Costs more |
| Not proved to be Energy efficient or cost saving. | Reduces air conditioning costs by 50 to 90% |
| No effect on home resale value | Increases home resale value |
| Most effective at the hottest time of the day | Most effective when the outside temperature is lower than the home temperature. |
| Can be used along with air conditioning | Cannot be used along with air conditioning |
What are whole house fans?
Whole house fans are exhaust fans installed on the ceiling of the house ie, the place between the attic and the living areas of the house. So how does a whole house fan works and why is it installed? A whole house fan pulls hot air from the living areas of the house removing it to the attic. This creates a negative pressure inside the house which will cause the cooler air outside the house to come in through the open windows and doors. Thus, a whole house fan is used to cool a house when the outside temperature is lower than the in-house temperature.
Since this fan makes the house cooler, it significantly reduces the cost of running an air conditioner. If you want to know the math of it, I have made a detailed article.
As I said, a whole house fan is installed on the ceiling of the house. The ideal location is somewhere in the middle of the house, usually on the hallway ceiling so the fan can equally draw air from all the rooms.
Here are some pros and cons of a whole house fan;
Pros
- Reduces air conditioning costs by 45%
- It creates a nice breeze effect inside the house
- It is very cheap to run
- The cooling effect of whole house fans is much faster than an AC
Cons
- They can be noisy since installed so close to the living areas of the house
- Without proper winterization, the fan can cause heat loss through the hole in the ceiling
- It can bring allergens and dusts from outside
- Not ideal for humid climates as the fan will increase humidity in the house
What are attic fans
Attic fans are exhaust fans installed on the roof or the gable of a house. It is used to vent the hot air inside the attic. By venting the hot air inside the attic, the fan creates a negative pressure that pulls in cooler air from the outside through the inlet vents of the attic (mostly soffit vents or gable vents).
But why remove hot air from the attic, what can it accomplish. The fact is that normally the air inside the attic will be much hotter than the outside temperature since sunlight falls directly on the roof. This additional heat can seep into the living areas of the house thus adding extra load to the air conditioning system. By cooling down the attic to the normal day temperature, you can save on some cooling costs.
Here are some pros and cons of attic fans;
Pros
- Improves the life of roof shingles
- Easier to install than some passive ventilation systems like ridge vents.
- Makes indoor cooling faster by reducing the attic temperature
- Helps to ventilate the attic during winter to reduce mold growth.
- Improves the overall air quality in the attic
Cons
- No significant impact on air conditioning costs
- Without proper intake ventilation, an attic fan causes the conditioned air to leak into the attic
Comparison of the whole house and attic fans
Size
Since attic fans are used to remove air from the attic they don’t require to have very high airflow rates. The approximate CFM calculation of an attic fan is 0.7 x the square foot area of the attic. So for an attic with an area of 1000 sq. ft, the CFM needed for the attic fan would be 700 CFM. Refer Attic fan size guide for further info on this.
On the other hand, the CFM of whole house fans needs to be considerably higher to cool living areas. A general calculation would be a 2.5 x sq. ft area of the house. So a house with a 1000 sq. ft area will require a whole house fan of 2500 CFM. Experts require that whole house fans should do 3 to 6 air changes per hour for effective cooling. Since their CFM ratings are much higher than attic fans they are also bigger in size and have more power consumption.
Installation
Attic fans are relatively easier to install than whole house fans. If you have enough gable vents all you have to do is fit the attic fan on the vents. Rooftop installation is a bit more difficult since you will have to cut a hole on the roof and properly insulate it after the installation.
Whole house fans are installed on the ceiling between the attic and the living areas. You will need to cut a hole in the ceiling and make sure that everything is air-tight after the installation.
Quietness
Since attic fans are installed on the gable or the rooftop which are away from the ceiling, the noise from them is hard to reach the living areas. As a whole house fan is installed on the ceiling, the noise it makes will reach you much easier. Since whole house fans are also much more powerful they will make relatively more noise.
Today there are many whisper-quiet models available for both types of fans so my advice is not to worry much about noise.
Refer: Quiet whole house fans, quiet attic fans
Installation and running costs
Considering that whole house fans need to be bigger and more powerful compared to attic fans to cool the same area the former is going to be definitely expensive. The cost of attic fans ranges from 80 to 400 USD whereas that of whole house fans ranges from 150 to 500 USD.
Whole house fans are energy efficient and they cut air conditioning costs
Whole house fans are proven to be energy efficient and they help to reduce air conditioning costs by 50 to 90%. This reduction depends on the state you live in. If you are living in a hot location (temperature-wise) then you may be able to cut costs by 50-60%. In colder areas, you can save way more on air conditioning costs.
Attic fans on the other hand are not proven to be either energy-efficient or cost-cutting. They help in reducing attic temperatures but there is still no evidence that they are cost-effective.
Impact on the resale value of homes
In the right climate, having a whole house fan can increase the resale value of your home. By right climate, I mean moderately cool climate like in the North West of the USA. In those areas, a whole house fan can reduce air conditioning costs significantly during summer.
But attic fans, since they are not proven to be cost-efficient, don’t affect home prices. Having an attic fan won’t do any harm but as far as I know, they don’t play any role in the resale value of a home.
Best times to run
Attic fans are meant to cool the attic by venting the hot air in it. During peak temperatures, an attic can be unbearably hot. If there is no air circulation then the temperatures in the attic will be higher than it is outside. Therefore running an attic fan at peak temperatures will help to cool down the attic very fast.
Whole house fans are most effective during nights and evenings when the outside temperatures are cooler. As whole house fans draw this cool air and circulate them through the living spaces the temperature inside the house will lower quickly.
Attic fans can be used while the air conditioning is running but whole house fans cannot
Provided there is no air leakage between the attic and the living spaces, an attic fan is perfect to work with air conditioning. By reducing the temperature of the attic these fans help to reduce the load on air conditioners, slightly.
Since whole house fans suck air from the house into the attic, they cannot be used along with air conditioning. These fans are to be used before you switch ON your air conditioner. When you run the whole house fan, it reduces the temperature of the whole house so an air conditioner does not have to work very hard.
How to tell if you need an attic fan or whole house fan
Whether you need an attic fan or a whole house fan depends entirely on your requirements. Both fans fulfill different requirements, hence one cannot replace another. If you are looking for cutting down your air conditioning bills I recommend you install a whole house fan. But not if you live in a humid climate.
If you have problems with your attic ventilation, then you should buy an attic fan. Lack of attic ventilation can affect the life span of your roof, cause mold growth, energy loss from HVAC ducts going through the attic, and many other issues.
Using both of them together is also a good idea as the attic fan will help to ventilate the air moved to the attic by the whole house fan. But again, this depends entirely on your requirements, installing too much attic exhaust ventilation without sufficient intake vents will only worsen the situation.
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