Upgrade from 2 ton to 3 ton unit

[Daniel Hsieh]

I am selling a home and a buyer is saying my house is 4200 sqft and one 2 ton unit and one 3 ton unit is not powerful enough for the house and he wants to ask for 5k discount because of that. I am not very good at Ac quoting. Is 5k too much is swap out a 2 ton for a 3 ton unit? Is the request even reasonable?

[Jim Adrian]

This is pure speculation on his part, though he may be right.  Without design calcs from mechanical engineer or an hvac company I would not honor his request without proof.  Oversizing the units can cause more problems, bigger isn't better in this case.  The system wont cool correctly when over sized and the equipment will constantly cycle causing the unit to burn up. It also has to do with how the ductwork is laid out short runs vs long runs. 

If they are only asking for $5k off the asking price because they don't like the equipment and the rest the deal is good, then consider taking the offer.  I would let him replace the units on his dime no matter what.