Whole House Fan: A to Z Guide to Cooling Your Air
While we most commonly think about an air conditioner as providing much needed relief in the summer, there is another way to cool your home.
We’re talking about a whole house fan.
To start, we’ll explain what a whole house fan is and how it compares to an air conditioner in your home.
Then, we will go into helping you to choose the right size of whole-house fan and how to install the system.
So, let’s begin.
What is a whole house fan used for?In simplest terms, it is a type of air conditioning.
A whole house fan is a large fan in the attic of a home. It pulls the hot air in your house into the attic. From there, a pressure is created in the attic and the hottest air in your attic is then pushed out through attic vents in the roof. It also serves as a whole house ventilation system.
The system is installed in the attic and is connected to the ceiling of the highest floor.
How does a whole house fan work?It works from the principle that hot air rises. With the pull of the fan, this natural process is enhanced to where cooler air is drawn in from outside.
So, with windows open in your house it can quickly cool down. It also provides good ventilation and can improve the air quality in circulating out stale, polluted air.
There are a couple things to keep in mind.
One, this works best in areas where the outside air cools down in the evening and has lower humidity levels. It’s not a good solution in Florida in the summer where it tends to be hot and humid but can work well in most other areas.
Two, you need to have an attic to store the whole house system as well as to be able to open windows so the cooler air can be drawn in.
Air Conditioner vs Whole House FanWhile an air conditioner and whole house fan both serve to cool your home, they work in very different ways.
An air conditioner can be a window unit, portable ac or a ducted air conditioning system (or HVAC). All air conditioners use a chemical like Freon that changes between a gas and a liquid to transfer heat from the inside air to outside.
While a window AC pulls in air from the outside, a ducted air conditioning system circulates the air within a home. So, a central air conditioner will cool down the air and reduce humidity levels however it will not pull in fresh air from the outside.
A whole-house fan does not have Freon, a compressor or condenser like an AC. It’s just moving air.
Whole house fans are often used to supplement an air conditioner. That is, when the conditions are right it offers a better way to get cooling.
Advantage of Whole House FansThese systems are becoming more popular because they can use 90% or less energy than an air conditioner. They are significantly more energy efficient.
An air conditioning system in the home makes up about 50% of a monthly energy bill. So, it doesn’t take long for the fan to pay for itself.
Because of this some states have begun to issue rebates to homeowners to encourage the use of the fans.
Another advantage is the improved ventilation. Indoor air can be many times more polluted than outdoor air. So, by pushing out the poor indoor air with cleaner outdoor air can be a big improvement to your indoor air quality.
It provides much better cooling than a ceiling fan. Ceiling fans move air within a room however they do not pull in cooler air from outside nor do they help with ventilation.
How well do attic fans work?Another name for whole house fans is an attic fan. They work very well provided they are used in the right climate, sized properly and correctly installed.
First, as mentioned earlier, the air outside needs to cool down since you will be pulling in the cooler air from the outside. If it is hot and sticky outside, this is what you will be bringing into your house.
Second, the attic fan must be sized right to be able to move enough air for the size of your home. We will go into more detail about this below.
Third, while DIY’ers can install an attic fan system, some people choose to have a professional install. We give an overview for this below. It’s also important to note that by pulling air into the attic, you will want to have proper attic ventilation through the roof. This will allow the hot air in the attic space to naturally rise and vent outside.
Finally, for clarification some people refer to the vents on the roof as an attic fan if it has a fan motor. This attic ventilator is different than a whole house fan since it only pulls out the hot attic air and not the air within the home. For most homes the roof vents use a gable vent which is the name for the metal piece that you can see.
How big of a whole house fan do I need?It’s relatively easy to calculate how big of a system you will need. Follow the simple 3 steps below.
The first step is to know the air volume in your home.
1. Determine the square footage in your home. Do not include the basement area. If you have high ceilings increase the square footage number to account for this. We base the calculations on a standard 8’ ceiling height. If you have 10 ft ceilings then increase your square footage number by 25%.
2. Multiply the square footage by 2. This represents the CFM of the fan that is needed to cool your space and what is chosen by most people.
For example, if your home is 2,000 sq ft then you will want a 4,000 CFM fan.
If you are looking for greater air flow you can use a higher CFM system. In this case, multiply the square footage by 2.5 – 3.0. However, be sure to see step 3 to make sure you have sufficient roof ventilation.
3. Check the area of the vents in your attic. There should be at least 1 square foot of vent area for every 750 CFM of the fan. In short, make sure the attic air can properly vent for the amount of air that will be pushed into the attic. If the total vent area is too small you (or your professional) should increase the vent area through the roof.
Going back to our example, if the fan moves 4,000 CFM then you will want 5.3 square feet of vent area (4,000/750).
In shopping for a whole house fan, you should look for a system that can achieve the needed CFM’s. If your home is large this may mean you go with two systems to get to the require air flow.
We also recommend you consider the noise level. While you will want to move a good amount of air, no one wants a wind turbine in their ceiling. These systems can be quiet, just don’t forget to check on the noise level.
What is a CFM in a fan?CFM stands for cubic feet per minute. It represents the maximum amount of air flow of the fan. As described above, the CFM that you should look for is related to the size of your home.
Some systems have multiple fan speeds. This gives you flexibility in dialing down the air flow to reach a level that is ideal for your environment. A lower fan speed also means it is even quieter.
Whole House Fan InstallationIf you are a DIY person, you should be able to install the system by yourself. It should take a couple to a few hours. If you are not confident in your abilities then go with a professional.
Here is a video that shows how a whole house fan system is typically installed.
Be sure to follow these safety instructions for attic fans:
1. Cut the power at the circuit breaker or main fuse box. Test the wires to ensure there is no current.
2. Adhere to all local codes. If in doubt about anything contact a qualified electrician.
3. Follow the manufacturer’s installation instructions. Install in the proper location and ensure there is sufficient support for the fan and no obstructions.