A Manual J load calculation is how all heating and cooling brand manufacturers recommend installers size heating and cooling equipment. Manual J is from ACCA (The Air Conditioning Contractors of America) and is a square footage multiplier based on construction types. It is the only way to guarantee equipment sizing. Any other method is just a guess. If someone is sizing heating and cooling equipment without Manual J, they are guessing.
AFUE is the Annual Fuel Utilization Efficiency percentage. It is the amount of heat you get from every unit purchased. So if you buy $1 of natural gas for an 80% efficient furnace, you get 80 cents in heat and the other 20 cents goes up the chimney.
SEER is the Sesonal Energy Efficiency Ratio and is like miles per gallon on vehicles. The higher the number the less energy the system will use to cool your home.
R22 is also known as Freon and it is what is inside your air conditioner. It flows from the inside to the outside units, removing heat from the inside and depositing it outside. R22 is harmful to the Ozone if it is released into the atmosphere. That is why by 2010, you will no longer be able to purchase an air conditioner that uses R22. It will still be available for service of exisiting sytems, so you will not be required to replace your current R22 system if that is what you have.
R410 is what is replacing R22. It is Ozone friendly, so if it is accidentally released it will not damage the Ozone.