Base temperature

Climatic zones Conventional external temperature
H1a -9ºC
H1b -9ºC
H1c -9ºC
H2a -6ºC
H2b -6ºC
H2c -6ºC
H2d -6ºC
H3 -3ºC

Altitude (m) Correction (ºC)
Altitude < 400m 0ºC
400 < Altitude < 800 -2ºC
Altitude > 800m -4ºC