I am renovating a bathroom, and decided to install a combination heat lamp/exhaust fan as the room had no venting before. The unit has a 4" hose to connect to outside, with a damper at the unit. Where I live it gets down to below -35°C during the winter, and so far this vent is acting as a nice cold air duct. The unit is installed in the ceiling with an attic space above it. It is rated for insulation, so it is currently covered, but cold air is still coming in through the pipe. Any suggestions? I don't need any more cold air coming into the house, especially not where I will be standing soaking wet after a shower.