Yes bathroom exhaust fan ducts should be insulated and they need to be insulated well.
Does bathroom fan duct need to be insulated.
Can you oversize a bathroom fan.
The minimum allowed fan size is 50 cfm so if your bathroom is for example only 42 square.
Insulate the bathroom exhaust vent fan ducts.
Insulate the bathroom exhaust vent fan ducts.
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If these fan ducts are not insulated properly or not at all you will probably experience an excessive amount of moisture in the bathroom which can lead to other issues like mold.
We do not recommend purchasing vent ducts with insulation on the duct interior.
Second if your bathroom has a jetted tub or separate rooms or alcoves you might want more than one fan.