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do you mean my duct run is too long?....i'm not sure where you get the
14" measurement from.

The 3 " duct size fits the opening perfectly on the housing.

My error...your stated 3" duct size led me to believe it was 3" round
ducting. It must therefore follow, that your outlet size is 3" x 14"
rectangular. That being the case, keeping the troubled area warm by
insulation and heat tape may solve the problem. The heat tape
logically would be be powered by the fan circuit. So far as which to
try fist, the heat tape would be much easier to install. If it does
the job, quit there. If you judge that some insulation might help, go
for it.

Je