WindowsDepending on the age of the home and the type of windows installed, there are several different things that can result in energy losses. First, glass windows without any UV (E-glass) protection can cause the rooms in the home to heat up when exposed to direct sunlight. Sure, this is great for those cold winter days, but in the summer, it causes your air conditioning to run longer and more often, resulting in increased energy usage.
Next, depending on the materials the windows are made of, they could be transferring heat or cold from the outdoors into the home. Aluminum windows are a good example because the metal gets warm or cold and is susceptible to temperature changes. So, the window frames could actually be lowering or increasing the temperatures in the rooms within your home. Lastly, the age of the windows can result in broken weather stripping and caulk creating air gaps where the heated or cooled are from inside the home can escape and also allow air in from the outdoors. If you notice air drafts around the windows, you have an air leak and are losing energy.
Doors are also a cause of energy loss for homeowners. For instance, sliding glass doors consist mostly of glass so there is the heat/cold transfer if the glass is not an E-rated glass. Next, the fit of the door around the doorway can leave small openings where air can get out and in the home. A good test is to see if you notice light coming in around the doors and if so, this means the door does not properly fit in the doorway. Lastly, doors do wear out over time from constant exposure to the elements and hot and cold temperatures. Depending on the type of materials the doors are made from, they can slowly warp and eventually will no longer fit correctly around the doorway. A good indication a door is warped is if it has gaps on one side and fits tightly in other areas, where you have to lift or push/pull on the door with added force to get it opened or closed.