Sealing your home against air leakage is one of the simplest things you can do to reduce your energy bills. Air leakage can account for 15−25% of winter heat loss can contribute to a significant loss of coolness when air conditioners are used. One of the ways the air can get out is through your ceiling exhaust fan.
When not in use, exhaust fans are really just holes which suck out your home cooling and heating. But all is not lost! There is now an exhaust cover available that can be fitted to your horizontally mounted exhaust fans. This involves valves which open automatically when the exhaust fan is switched on and shut again when the fan is switched off.
You will need an electrician to fit the cover.