Whole house fans are installed on the ceilings of the houses and they exhaust hot air from inside the house into the attic which in turn is vented to the outside via attic vents. So the movement of air is from indoors to the attic and then to the outside.
But not all whole house fans work like this. Instead of the ceiling, there is a type that can be mounted on the rooftop. These are called roof mount type whole-house fans. Roof mount whole house fans are those whole house fans that are mounted on the roof of the house, and they exhaust the indoor air directly to the outside without circulating it through the attic. So in this case the air movement is from the indoors to the outside without it going into the attic.
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How does a roof mount whole house fan work?
As stated before, a roof mount whole house fan exhausts the hot air inside the house into the outside. The fan is installed on the roof and it is connected to the interior of the house through an insulated duct. When the fan is switched ON, it draws out the hot air from the living areas of the house through the duct and exhausts this hot air into the surroundings. This removal of air creates a negative pressure inside the home which draws in the cooler air from outside through open windows. This process cools the insides of the house without the need for an air conditioning unit.
A roof mount whole house fan works just like a normal whole house fan except that it is mounted on the roof of the house and the air is sucked from the indoors via a duct that passes through the attic onto the roof.
Why not use a normal whole house fan instead of the roof mount type?
Roof mount whole house fans are there for a reason. Even though the majority of attics in the USA are vented not all of them are so. There are thermally insulated attics where there are no exhaust vents. In these cases, a normal whole house fan cannot be used as they vent the hot air into the attic space.
Therefore, a roof-mounted whole house fan is used if the attic of the house is insulated. In this case, since the air is directly vented to the outside through the roof, there is no need for attic ventilation.
Roof mount vs normal whole house fan – Quick comparison
|Roof mount whole house fan||A normal whole house fan|
|Mounted on the roof||Mounted on the ceiling|
|Air is vented directly to the outside||Hot air is vented into the attic which is then vented by attic vents|
|Difficult installation||Easier installation|
|Costs more||Costs less|
Can I use this whole house fan for a vaulted ceiling?
The problem with vaulted ceilings is that they don’t have an attic. In the rare case that they do, those attics are not spaced enough to install a whole house fan.
So unfortunately it is NOT possible to install a whole house fan on a vaulted ceiling. There are some models by Quietcool which can be installed on a roof with no attic however the company doesn’t recommend their use on a sloped ceiling as it can create a lot of noise.
Whole house fans for roofs without attics
As mentioned before there are some whole house fan models which can be installed on the roof even though there is no attic space. This is one such model from Quietcool Systems – RM WHF-4.0. Some variations of this model can be installed on insulated attics and flat roofs with no or little attic spaces.
Pros and Cons of roof-mounted whole house fans
Just like everything, roof-mounted whole-house fans too have some pros and cons. Here are they;
- Best choice for insulated attics
- Quieter operation as the fan is installed much farther away from the living areas
- Roof mount fans cost more than normal models
- They are more difficult to install, you need to cut holes in the ceiling as well as the roof
- Not many models to choose from
Additional reading: Ducted whole house fans