Ross Herbert said:
SNIP
:
:Unless you live in Tasmania, one fan type roof vent is not enough. They are
:cheap, and can be easily blocked in winter, (and the blades fixed) which is
:what I do.
It also depends on the volume of air which must be exhanged in a given time in
order for any cooling effect to become meaningful. As you say, a single vent is
far from ideal but I would have thought that a fan driven vent (Powervent) which
is quoted as being capable of exchanging 250L/s would not take too long to
remove and replace the air volume in my roof space. Passive "whirly bird" type
vents don't move that much air and that's why you need 6 - 8 of them to provide
similar proficiency to the fan driven unit.
Yes, it was that type I was referring too, but they are cheap to buy, cost
nothing to run, and require no maintenance. So about four for an average
house is no big problem IMO. Nor is blocking/unblocking them twice a year
IMO. Your powervent will obviously work on a completely still summer day
however.
Most people don't use them simply for the same reason they buy halogen
downlights, they have no clue!
MrT.
