Recently, I had my bathroom remodeled. I selected and had installed a Braun bathroom exhaust fan. I worked great. Until I noticed my central A/C seemed to be running longer to cool the house. I did a kleenex test with the bathroom exhaust fan: With the A/C off, I turned on the exhaust fan and held a kleenex up near the grillwork. The kleenex sheet got sucked up tight against the vent. Turn off the fan, kleenex fell to the floor. I then turned on the central A/C and again held the kleenex up near the bathroom exhaust fan. Again, it got sucked up against the grill work. Apparently, my central air/heat system generates enough positive air pressure in the house to cause the bathroom exhaust fan to vent the conditioned air (read: dollars!!!) to the outside. I checked the vent on the roof while the A/C was on and the exhaust fan was shut off and felt cool air coming out the roof vent.
With the A/C and the bathroom exhaust fan both off, I have never noticed any air coming in from the outside, so I'm guessing the backdraft damper door is working.
I taped a couple of 8.5x11 sheets of paper over the exhaust fan grillwork and noticed over the next few days that the A/C was not taking so long to cool the house--we had consistent 100 degree days over a couple of months.
The grillwork now remains covered and the exhaust fan unused ever since (about 2 months now).
Anyone have a solution for this? Might it be possible to add a little weight to the backdraft damper so it doesn't open when the A/C is on? I was thinking washers or a penny or two epoxied to the lower or mid section of the damper door might work.
Thanks for any info anyone can provide.