Before you make a selection on sub floor ventilation systems it is important to know the sub floor layout of your home.
If your sub floor layout is a square or rectangular shape, brick size or terracotta vent size sub floor ventilation system can be used. This is because if passive vents are installed at the top side of the square (preferably on the north of western aspect) and the fan-forced sub floor ventilation system are placed at the bottom of the square (preferably on the south or eastern side) airflow will travel from top to bottom.
Cross flow sub floor ventilation is achieved as the drier air is ingressed through the passive vents via the sub floor area as it flows uninhibited toward the sub floor ventilation systems.
In this instance the use of in-line sub floor ventilation fans and flexible ducting is not warranted as it clogs the sub floor area space with extra materials.
In some cases a sub floor ventilation problem may only be confined to one area of the sub floor area of the home and if the outside ground level is lower than the inside floor level a sub floor ventilation system as shown above can be used.
If a musty smell is present and a sub floor ventilation system is put in place, the musty smell should cease to exist inside the home after six weeks or sooner. Entrapped humidity is being extracted via the sub floor ventilation system, this means that you are heading in the right direction.
What if the sub floor area is not completely square and you have another square section jutting out from it?
As mentioned earlier if the outside ground level in relation to the inside floor level is lower then the Envirofan sub floor ventilation systems as shown above can be used.
What if the outside ground level is higher than the inside floor level?
If you are going to embark on extensive landscaping you can lower the outside ground level if need be install retaining walls and sub soil drainage. Then sub floor ventilation can be installed.
However if no landscaping is to be undertaken the only option is to install sub floor ventilation systems with ducting.
Envirofan has the right kind of system for this situation as the quad fan system is installed into an adaptor and its grill is placed on the exterior of the building.
The other feature of this kind of sub floor ventilation system is that it is 12volt which means it has a very low power consumption or solarpower if desired. It also is probably the only sub floor ventilation system with low noise attributes at 27dba.
This configuration applies to a certain area and not necessarily to the whole house. The situation just described should be left to a sub floor ventilation consultant/installation person as after visual sub floor inspection will advise you accordingly.