SEER stands for Seasonal Energy Efficiency Ratio. SEER is one of those hard-to-understand acronyms but SEER is a lot like the MPG for your car. The savings you can achieve with a higher SEER is similar to gas savings with a car that gets a higher MPG. For example, if you have a car that gets 8 MPG (many older air conditioners are about 8 SEER) and you upgrade to a 16 MPG car (or a 16 SEER AC) you will be achieving 50% fuel savings (or 50% energy savings on your AC use).
AFUE stands for Annual Fuel Utilization Efficiency. This rating tells you how much of your heating dollars are converted to heat energy put into your home and how much is lost up the flue pipe. Most older furnaces are 60% efficient. That means that for every dollar you spend on gas from your utility company $0.60 cents is used to heat your home and $0.40 cents goes up the chimney. Federal law mandates that all furnaces being produced today be at least 80% efficient and many of our furnaces are 90% plus in efficiency. Oftentimes, if you replace an old, energy-wasting furnace the savings on your utility bills, will more than cover the cost of the new furnace.