WHICH REFRIGERANT: Today, the gas offered in residential is R410a. This was made mandatory for a system starting in 2010. In most cases, this will require a new indoor coil as well. It is wise to replace the refrigerant piping if you can as it it has been used with a different oil than R410a uses. If you can't change the piping, the dealer will need to blow out the old oil from the system. Many dealers use a flush agent to thin out the oil to make it easier to clean out. Now, manufacturers have found a loophole in the law requiring R410a. If they just sell an outdoor unit they can sell it empty for the dealer to fill with R22 and use on your old indoor coil. Any time you reuse an old coil, you have a mismatch in the SYSTEM and lose capacity and EFFICIENCY. So unless you have a very new coil, it would not be wise to consider the empty unit. R22 is currently over 5 TIMES the price of R410a and climbing.
EXTENDED WARRANTY? Most dealers are offering extended warranties on top of the manufacturer's warranty and their own labor warranty. Periods of 5 and 10 years are common. Should you buy? If priced competitively and from the manufacturer or a relaible 3rd party firm, it would make sense to, especially on furnaces. As furnaces are becoming very complex and many of the components are made in developing nations to keep the price down, repairs are becoming more common and more expensive. In 10 years if you plan to stay in your home, you most often will recoup the investment. Do read the fine print, however, as these warranties only cover breakdown of the equipment. Maintenance and problems not related to an equipment failure are not covered. If you purchase a warranty provided by the dealer, remember you are tied to that dealer and would not be able to switch service providers.