We had a similar problem in one of our bathrooms. When I would do my business in this bathroom, I would feel a cold breeze coming from the vent side of the vent/heater/light fixture. I did a little research on how the ductwork should be plumb and found that I could add a valve to the duct, simile to this:
This is upside down as it should be installed.
I decided to investigate and it was tough because I couldn’t easily access the area above this bathroom.
So I decided to remove the fixture and go that direction. When I did, I found that a one way valve was attached to the vent outlet on the fan. However, some jackwagon installed it upside down where it would remain open all the time. I turned it over and reinstalled the fixture, and no more draft.
The way that valve works is gravity will keep it closed because the disc is offset, but when the fan starts, the valve opens.
This is upside down as it should be installed.
I decided to investigate and it was tough because I couldn’t easily access the area above this bathroom.
So I decided to remove the fixture and go that direction. When I did, I found that a one way valve was attached to the vent outlet on the fan. However, some jackwagon installed it upside down where it would remain open all the time. I turned it over and reinstalled the fixture, and no more draft.
The way that valve works is gravity will keep it closed because the disc is offset, but when the fan starts, the valve opens.
We have vents in our bathrooms that have light plus heat. They let in a bunch off cold air as they vent in the attic. I cover them with the sticky type plastic wrap used in the kitchen to seal food. This stops a great deal of cold air from entering the bathrooms when it's cold outside and in the attic.
Been burning a bunch of firewood the past couple days which keeps the house at about 74 degrees without the electric heat pump kicking on.
Also covered the north windows in the master bedroom with plastic sheeting on the inside of the windows. Those windows get very cold when the wind is out of the north. Makes a great deal of difference on the temperature in the master bedroom.
Lots of great ideas on this forum for conserving energy and keeping one's house warm and economical.