Don't use rules of thumb to size equipment. The contractor should do a 'Manual J' calculation on the house to determine what is actually the proper size of equipment to install.

Having 'their own brands' they work with is normal. That's how they get approved by the manufacturer to do warrantable work, they agree to install their equipment and not other brands. That also gives them a lot of experience with that particular brand of equipment.

You want a reputable contractor that has been in business for a long time with plenty of happy, satisfied customers. You also pay for what you get.

"Having 'their own brands' they work with is normal. That's how they get approved by the manufacturer to do warrantable work"

Actually they "have their own brands" so that they can charge what they like - you cant get competitive bids because you would be comparing different brands - apples to oranges.

You need a properly conducted heating and cooling load evaluation. The sizes installed sound close but should be confirmed with a "Manual J" calculation.

"Having 'their own brands' they work with is normal. That's how they get approved by the manufacturer to do warrantable work"

No HVAC contractor that I know of is in this business for warrantable work?

The manufacturer doesn't pay for warrantable work. They provide a part to a licensed contractor. If that licensed contractor is claiming too many warranties, the manufacturer may start checking parts that contractor brings back. There could be a discussion at some point if parts brought back are not broken as claimed.

Some manufacturers are more challenging than others when it comes to getting reimbursed for defective parts... even if that part has already been exchanged for a new one.

Who in their right mind would then get into this business for the sole reason of trying to do warrantable work?

NO ONE.

Just because you read it on the internet doesn't make it true.

Extended warranties that pay labor: The work still has to be approved. You pay for that warranty and you're required to have the equipment maintained at additional cost.

Certain things are excluded from warranties: Maintenance, Refrigerants, & Freight (shipping)

Some brands to consider are Carrier/Bryant, Trane/American Standard. Rheem/Rudd, and Lennox. You should find out what are the common brands in your area and make a list of installers who are licensed and have good reputations. The quality of the installation is more critical than the brand. Top of the line equipment will never work properly if it is not correctly sized and installed incorrectly.

An installer should not be using a rule of thumb for sizing. That tends to oversize equipment. A 1550 sq. foot condo in your location should be do well with a 40K BTU furnace and 2 ton AC. The AC may have to be made bigger if you are exposed on all four sides and on the top floor. The installer should do a load calculation and also examine the duct work for proper size.

The sizes of the coil and the compressor have to be matched. The manufacturer determines which are the allowable matches. Usually they are the same size, but there may be allowable options to increase the size of the coil. You also want the matching manufacturer's coil and not a third party brand. The installer should provide an AHRI certificate that indicates the equipment is an allowable match.