In which cases do we insulate exhaust ducts?

in3 cases you have to insulte exhaust duct

1- if the exhaust duct carring haigh temrature exhaust media and passing through conditioned area

2- if the exhaust duct carring low temrature exhaust media and you will use it for heat recovery system

3-if tha exhaust duct passing through haigh humidety area you need to protect it against corrosion 

وأى حدمة يا عم محمد يوسف

Usually we insulate the exhaust piping to prevent the fume from accessing the condistioned zones also to protect condensation of water in the inside of the duct could cause some potential hazard and duct  deprication rate uincreased according to sulpheric and other Acids Formation in the duct 

 specially in garages so the purpose of insulate the ventilation piping first according to the projects .scope is to protect the spaces and the inside of the pipe 

If the exhaust or any other ventilation duct is passing throught the air conditioned space.