for whatever reason, watso cannot see what it is that you have, in the first post .
anyway, in a subsequent post, you are totally wrong (unless watso is totally wrong) and you made the following comment..
"The whirly birds of the past just operated by wind so if the wind didn't blow, then no heat taken from the roof."
it is simple logic, but the warm air rises - and escapes through the whirlybird opening .
watso had a whirly bird installed (in his own house) - but we also had a rental property, with an enclosed patio (or whatever) - and that became a sauna in summer - anyway, with the installation of the whirly bird (and with the removal of some of the eaves) then the enclosed patio became liveable ... indeed , it was unbelievable what the difference made
as watso types this post, he can look up (in an old house - and obviously the ceilings ) at the corners of the computer room (and the same for every other room) and there are vents that allow for the warm air to escape (not much good in winter) - but a whirly bird would allow the warm air to escape to the outside
