It can be hard to detect air leaks where cold air is blasting inside during the winter months, and the United States Department of Energy has two easy tips to find out if there are leaks in your house. First, turn off all the indoor and outdoor lights, and use a flashlight to shine on potential gaps inside the house. Have someone outside to observe the house as you shine the light; large cracks in the house will show up as rays of light. Second, grab a dollar bill and shut a door or window on it. If you can pull it out and it doesn't drag, the window or door needs to be weather-sealed.