What is a whole house fan and how does it work?

What is a whole house fan?

Whole house fans are exhaust fans that connect the living areas of a house to the attic. They are installed by cutting a hole on the ceiling, and they move hot air from inside the house to the attic thus cooling the living spaces.

Image of a whole house fan
Image of a whole house fan Source: quietcoolsystems.com

The purpose of using a whole house fan is to reduce the temperature inside the house by removing the hot air from the house and replacing it with cool air from the outside. It helps to reduce the load of the air conditioning if used correctly.

Whole house fans are usually installed in the hallway which makes it easier to draw air from the whole house. Yes, these fans are expected to draw air from the whole area of the house, and that is why they are rightly called whole house fans.

When compared to a regular exhaust fan, a whole house fan is much bigger and heavier. It will also draw much larger quantities of air. Unlike a regular exhaust fan whole house fans are designed to be installed horizontally. If you install an exhaust fan horizontally its bearings will heat overtime leading to damage and even fire hazard. I have seen several youtube videos where people use a box fan instead of a whole house fan but it won’t work like that for long due to the above reason.

The power rating of a whole house fan ranges from 3000 to 7000 CFM. A rule of thumb is to use a fan that has a CFM three times that of the area it need to cool. So if your house is 1500 sq.ft then a 4500 CFM fan would be the right choice. The size of the fan is also decided by the location where you live. The southern states of USA are very hot and if you live there you will be needing a more powerful fan.

I will be writing a detailed article on the size calculation of whole house fans soon.

Parts of a whole house fan

A whole house fan is very simple in construction. It comes with a fan and motor, a housing and a shutter. There can be aditional accessories and parts depending on the features of the fan you buy.

Types of whole house fans

There are mainly four types of whole house fans;

  1. Ducted whole house fans
  2. ceiling mounted whole house fans
  3. Roof top mounted whole house fans
  4. Direct drive fans
  5. Belt drive fans

Ducted vs ceiling mounted vs roof top mounted whole house fans

Types of whole house fans

A ducted whole house fan is a relatively new type which use a duct between the fan and the louvers. In this case the intake grill will be installed by cutting a hole on the ceiling and the fan will be installed by hanging it from a rafter of the attic. The duct is usually 6 to 10 ft in length so it won’t be hard to find a string rafter within that length.

Here is a video showing the installation of a ducted whole house fan;

The benefit of using a duct type whole house fan is that it will be much quieter than a regular model. Since the fan is installed away from the ceiling you won’t be hearing any sound from it. It can also draw air from multiple locations with the use of suitable accessories. This type of fan will cost a bit more but the installation is as easy as installing a normal whole house fan which makes this a popular choice for many.

Non-ducted or ceiling mounted whole house fans are regular ones that don’t have a duct. The fan is installed directly over the louvers. It is fixed on the joists. The working of both types of whole house fans is the same but this one will be noisier than the other.

Here is how a ceiling mounted whole house fan is installed;

Roof mounted whole house fans are those which are installed directly on the roof of the house. They are used when the house has no attic. They are basically roof mounted attic fans.

Direct drive vs belt drive whole house fans

In a direct drive type whole house fan, the motor and the fan are connected directly ie, they share the same axle. In this case, the fan will rotate at the same speed as the motor. They are also more energy-efficient since there is no slip between the motor and the fan. They also tend to last longer due to the absence of any tensions between the moving parts. One problem though is that these tend to be slightly louder than belt-driven fans.

A belt-driven whole house fan has a belt connecting the fan to the motor. The motor is placed a little away from the fan but without obstructing its working. Belt driven fans are slightly less noisy than direct drive fans. This also allows for flexibility in fan speed. Their downside is that they could be less energy efficient when compared to direct drive fans.

Standard cooling vs Breeze cooling

The cooling effect by whole house fans can be divided into two; Standard cooling and Breeze cooling.

Standard cooling is when the whole house fan changes air around 30 times an hour. It won’t draw large amounts of air so the cooling of inside the house will be slower. These fans are generally low powered and needs only a CFM value 1.5 to 2 times the area it needs cooling.

Breeze cooling refers to faster cooling by whole house fans. Here the number of air changes will be high (up to 60 times an hour), and the power and the CFM rating of the fans will be higher as well. A CFM rating of 2.5 to 3 times the living space area is recommended for breeze cooling. While the fans operate you will feel a breeze inside the house, and that’s why it is called breeze cooling.

How does a whole house fan work?

A whole house fan is used to cool the living areas of a house when the outside temperature is lower than the inside temperature. The whole house fan works by moving hot air from the living areas to the attic thus creating a negative pressure inside the house. This negative pressure will draw the cool air from outside through the open windows which in effect will lower the temperature of the house. The hot air moved to the attic will be vented through the soffit and ridge vents of the house.

A diagram showing how a whole house fan works.
Working of whole house fans

Here is a video showing how a whole house fan works;

Please note that whole house fans are effective only when the outside temperature is lower than the temperature inside the house. Make sure to open the windows before switching it on. Using attic fans in combination with whole house fans is also a good idea. Attic fans make sure that the hot air moved to the attic is removed immediately. This will make the cooling of the house faster.

Whole house fans help to reduce the cost of air conditioning by 50 to 90%. This reduction depends on where you live. If you live in the southern states then the cost reduction may be only around 50%, the cooler your area is the more you can save with a whole house fan.

You can check my list of the best whole house fans if you are planning to buy one.

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