Can this be done A/C setup

[dante2]

We have a home that was originally 1600 sqft and in the 90's another 600 sqft room was added on in the back. The main part of the house has a 2.5T unit and the add-on has a package unit 2T I believe. All registers are in the floor and the house is on a slab. These units are getting up there in age and replacement time is closing in, been doing minor fixes as they come up. Would it be possible to install a larger unit in the main part of the house and connect to the add-on to eliminate the package unit all together? The package unit is on the north wall and is approximately 60' from the main unit. Wife isn't excited about a mini split in that room so that's currently off the table. This is currently just a thought and I was wondering if it was even possible.

 

[Ohmthis]

I’m not gonna lie, with all of the ductwork in the slab, this sounds like a horrible job. Is the addition on a slab as well? Is there open attic the entire way? It might be better to make a new duck system in the attic and use the old supplies in the floor as a return. Sizing might be so totally wrong for that though.

 

[dcg9381]

Would it be possible to install a larger unit in the main part of the house and connect to the add-on to eliminate the package unit all together? The package unit is on the north wall and is approximately 60' from the main unit. Wife isn't excited about a mini split in that room so that's currently off the table. This is currently just a thought and I was wondering if it was even possible.

Really hard to answer your question without knowing the duct sizing, layout, and design... And how much space you have for a single (larger) air handler. Definitely a "local" need-eyes-on-it job.
Ductwork in the floor, but house is on slab? Is there a craw-space? Never seen a concrete foundation house where ductwork is in the slab. If I understand that right, you can't change this design at all..

Can you talk the wife into a "ceiling cassette" mini-split system? I assume it's that wall unit that she doesn't like...

 

[mm08822]

I'm no HVAC guy but I would be concerned about trying to add load to the existing ductwork to supply the addition.
Unless you go the attic route to get to the 600 sqft addition, I think you will destroy any balancing that may exist in the home. The addition could also be starved.
60' also adds in some challenges for temp measurement and correction. Put the tstat in the wrong place and you may starve an area.

2T sounds high for 600 sqft......maybe it is correct, but a load calculation (heat and cooling) would confirm. Both areas should get a refreshed calculation.

I suggest you spend some time detailing each existing system: ESP's, ductwork sizing, lengths, existing fanspeeds (CFM), even fuel consumption of each (wait for winter, though).

Also heat loss/gain data: wall/floor/ceiling/window areas, insulation values. Having this physical data is the needed legwork for the heating/cooling calculations (1 reason why most never do it.) and demand for each register.