Most people take for granted the comfort provided by their central air conditioner, heat pump or furnace until something goes wrong and the system needs to be serviced or replaced. For most of us, the understanding of our home air conditioning and heating begins and ends with the thermostat. We turn it up for heat and down for cooling, but we�re not exactly certain how or why it works the way it does. This can be a disadvantage when making a purchasing decision. As an informed consumer you can make better decisions about your home comfort and needs.