In buildings that use the sun as a heating source, the most important element of design is a southerly exposure, and windows are the most common form.

An essential component of conserving energy is keeping conditioned air in your house and keeping unconditioned air out, meaning that in the winter hot air doesn’t escape and in the summer cool air doesn’t escape. Insulation plays a role in keeping your house warm too, but regular fiberglass insulation does not stop the flow of air. Typically insulation is effective at preventing heat transfer through materials (limiting your home’s ability to conduct heat), it cannot prevent air from actually sneaking in and out through holes and cracks. (The exception to this is sprayed-in Cellulose and some foam insulations that can both air seal and insulate)