Every home has windows; their placement will decide how much light and breeze they will let in. Though you may enjoy keeping the windows open at some times of the year, there will be times when it’s either too hot or too cold to do it. This is when you should shut them and use either the heating or cooling function in the HVAC system.
The fact is that heat that transfers through the windows can easily account for 10-25% of your air-conditioning and heating costs and the biggest culprits are the older, single-paned ones. The one way to prevent this from occurring is to replace them with double-paned energy saving windows. Though the latter isn’t going to be very light in your pocket; the long-term benefit is that they can reduce your energy use by almost 30%.