Thanks for all of the input.
2. A inside wall unit is not a Central HVAC unit.
3. The addition of the 350' sunroom would need to have: 1) permits pulled, 2) a footer and slab poured, 3) the exterior siding has to match the existing siding and 4) the Home's current HVAC would need to be ducted into the addition and still handle the additional sqft to be included in the livable sqft of the home, in my experience.
If a back patio was built in and not all the steps in #3 were followed, a seller would have a hard time convincing a buyer that this 350' is worth what the market average is of the neighborhood to be included in the pricing.
At most, if not all requirements of #3 are meet, that a seller can try to include Â½ of the patio build-in, at most.
All situations, buyers and sellers are different and Real Estate is a Market, any sqft measurements that are different the county records are placing all parties in a difficult situation. I recommend having a sqft measurement service come out and provide you w/ their opinion so that you can better establish your argument, as to this sunroom being or not being included.
Hope this helps,
Josh Barnett, Realtor
Metro First Realty
I hope this helps.
Best of luck!