We are about to start adding a 400 sq feet addition to our just purchased to-be rental property that is 1000 sq feet, so 1400 sq ft. total. The property is in NE Ohio, so we get heavy snow and cold and humid summers.
In this house we are: Replacing the 17-year old gas furnace with a high-effeciency unit. Abandoning our in-slab forced-air ducts and putting in attic ductwork in both the existing space and addition. The 3-year, 2-ton rated air conditioner compressor we are going to keep - the HVAC guy said it may be underpowered, but since it is so new we are going to see how that goes. The interior is going to be a total gut, from the flooring to the attic, so anything goes and I'm not worried about anything getting damaged.
Since we are changing out the furnace though and changing the direction of the airflow from down (into the slab ducts) to upwards (into the new attic ducts) he is suggesting we change out the evaporator coils to one that is rated for 2.5 tons in a upwards direction. He says that he has seen issues with just flipping over evaportor coils, and if we do decide to upgrade to a 2.5 ton compressor, we would have to upgrade the evaporator coil as well.
This is an additional $1200, which is inline with an evaporator replacement. What I want to know is a) what he is suggesting makes sense, and b) are there issues will running an over-sided evaporator vs. the compressor? I'm more concerned with this being done right than cheaply.