I do believe that many/most if not all of the UK met office temp housings are normally aspirated, many in stevenson screens
some at airports in other shields, I feel the fan idea is a must for most back garden enthusiast due to the obstructions. Official
sites have uninterrupted sensor placements, no trees, no buildings, no hills etc, then there is the height of the grass, even that
can make a difference, having a fan can make up for some of our less fortunate sensor placings, I myself had to go 24hr fan
and still had to place it on the mast (13ft est) and i still think i maybe slightly above during the afternoon when there is little to
no breeze but no so much when there is some decent winds.
The image below is of 3 RAF bases, only Marham (EGYM) is the offical Met Office station but, the other 2 are still used
when looking at extremes, i.e. if Lakenheath (EGUL) was the hottest place in the UK it would be still mentioned regardless
The pink line is a Davis Vue, the day was yesterday and it was very breezy, 30mph+ gusts. The second image is minimal winds
bear in mind i am running a 4k rpm PC fan at 12v (VP2 Plus bought feb this year)
D7935: 1.6 miles (Lakenheath, UK: lat 52.4417, long 0.5982, altitude 14 metres)
EGUL: 4.3 miles (Lakenheath Royal Air Force Base, United Kingdom: lat 52.4093, long 0.5610, altitude 10 metres)
EGUN: 8.8 miles (Mildenhall Royal Air Force Base, United Kingdom: lat 52.3619, long 0.4864, altitude 10 metres)
EGYM: 12.9 miles (Marham, United Kingdom: lat 52.6483, long 0.5670, altitude 23 metres)