Crawl Space Ventilation – ‘To Duct Or Not To Duct’

Crawl Space Area

Crawl space is an American term which refers to the sub floor area. No matter  what terminology is used, it is equally important to get the sub floor ventilation right.

It is said that ‘A picture paints a thousand words’ the picture shown has been modified to show 150mm duct in the sub floor area. But the question needs to be asked ‘Why put a duct within a duct?’ Or let us go one step further and ask ‘Why put a duct within a duct whereby the Envirofan quad fan system could be installed in the opening in the extraction mode, where the sub floor area could act as an air transfer duct?’

With solid brick construction the principle of air extraction would be the same as in brick veneer construction, the difference being that since room are sectioned (as shown below) off from one another by sub walls each room would need its own ventilation systems to draw the damp air out creating extracted air in the sub floor region and forcing it into the next chamber.

subwallsA perfect example of this is illustrated in the diagram on the right as the brick size Envirofan is installed in the foundation walls without the louvered grill in the sub wall between the two rooms, utilizing the crawl space area as the air transfer duct. If passive vents were placed on the left and right hand side exterior walls this would allow fresh air to ingress into the sub floor area then to be fan-forced into the smaller chamber whereby the external Envirofan could complete the cross-flow process by drawing the damp air out. Is the use of flexible warranted in this situation? In the colder regions of Australia ducted underfloor heating is used whereby the warm ducts comes in contact with the cold ground especially with crawl space reduced clearances. This combination is a recipe for condensation on top of poor sub floor ventilation which is a twofold problem. Why use ducting for sub floor ventilation which adds to more unnecessary paraphernalia to the sub floor region? Envirofan sub floor ventilation systems have the simplicity in not clogging up the sub floor area. However there are some exceptions to this rule, which can be found under the heading ‘Cul-de-sac Ventilation’ heading which is found at:

With the numerous amount of installation that we have done, crawl spaces with vents are usually below floor level and above ground level are the norm. Reduced sub floor clearances areas cater for thirty percent of installation done, which do not represent the whole of house sub floor area, it is only present in a certain section of the sub floor area. So however the sub floor present itself, it is not a matter of one size fits all. Or in other words flexible ducting should just not be the standard procedure in sub floor ventilation. Envirofan has the right mix in maximizing sub floor ventilation by utilizing tc (terra-cotta) vent size and brick size ventilation systems. But will do what is necessary to get sub floor ventilation circulating in those ‘cul-de-sac’ or ‘dead’ areas.