The old line set (copper tubing) can be reused assuming it is the correct size of the new system. If not then it needs to be replaced. It is not the preferred method, but it is done where replacing the line set is difficult. The new refrigerant will be R410. The old refrigerant (R22) must be flushed out of the old line set otherwise you have a contamination problem. This is another reason why it is good practice to replace the line set. FYI - we can talk about prices all day long on this forum. Be warned the lowest bid usually comes with the highest risk. Finally this has been beaten to death, but let's make sure you understand the concept. You can use a 3.5 ton air handler with a 3 ton condenser. The important thing is the air flow is adjusted to the correct speed. The 3.5 ton rating is the maximum air flow, not the minimum. In turns out in this case the 3.5 ton air handler has better efficiency numbers than the 3 ton air handler. If the bigger handler can physically fit in the space, then you can use it. You have to then decide if the extra efficiency is worth the extra upfront cost of the equipment.

A reputable HVAC (Heating, Ventilating and AirConditioning) company would do exactly what is needed as well as your existing oil company. My advice would be to have whoever regularly services your equipment, to do the job since they will also be servicing it in the future. You can usually ask them that since they do all the servicing anyhow, is there any lower cost incentives they can offer if they do the work. There's a couple of things they may do....give a good deal on the repair, discount your service policy for the coming year, discount the cost of your oil a few cents.

'Offering a dependable product at a competitive price to the dealer should be far superior than sending them on cruises etc.' The manufacturer is there to sell equipment, that is how they make the bulk of their money. The more a dealer sells for the manufacturer, the more the wheel is greased. It always becomes about money or what you will get for what you do when it comes to a major brand piece of equipment. It really comes down to what a companies motivation is... working for the sake of your customers or bilking them. Pretty much every major brand is influenced this way. But you know people are people and many are influenced by the name on the sticker to one degree or another. There is value and then there is 'perceived' value. What is dependable? What is competitive? What is properly installed? When things have no true definition or meaning people wind up comparing apples to oranges and bananas.

Thanks very much for your reply. The upstairs is 1100 sq ft. The main level is the same, as is the basement. The upstairs furnace is 50 BTU. The heating is natural gas. There is ductwork in the basement that supplies the main floor. The basement is unfinished currently. That may change. There are six vents upstairs with one return in the hall area. The return is 12x24. There are eight vents downstairs with one return in the hall area. The return is 12x24. I was told that the unit upstairs had a leak/crack in the compressor that could possibly leak carbon monoxide. There are marks on the outside of the unit that looks like burn marks. The heating unit performed fine the last time we used it before we found out about the burn marks. It is about 25 years old and about 8 SEER. The cooling unit seems to run almost all of the time in the summer. The downstairs unit also performs ok but needs a serious duct cleaning due to water from a pipe bursting in the kitchen getting into some of the ducts. We haven't used it in quite a while. The house has humidity problems sometimes (window condensation and my indoor hygrometer can get near 80% in the summer but is around 50% in the winter) and we would like a system that can take care of that and be more efficient. The upstairs unit seems to run all of the time in the summer. The stat is usually set around 75. I was told that 16 SEER two-stage would fit the bill. Other ac companies told me I needed nothing more than the typical 13 SEER. Some family members have asthma and I also want something that will help with that. How can I tell if my ductwork really needs to be enlarged? Thanks much for your input