Are you sure the Carrier ANA7 has a recip compressor and not a scroll??
I think the NA7 was a typo. Carrier hasn't utilized the recip for quite a while inlcuding with Payne (but I am not a Payne expret..my apoligizes in advanced if wrong.) Most manu have made transition, even Trane/Am Stan has made the transition in upper SEER, However, we all remember Snow Ball so I may be wrong here as well.
Although one manufacturer was disparaged over another, it is your installing contractor and their abilities that make the system work as designed. I do have my personal opinoin and what I am comfortable with. However (you knew it was coming) there is one fact I cannot get around..and we spend alot of time this board communicating this fact. A sub par unit when installed correctly will perform great and last way beyond the "serviceable" life. A name branded unit, such as Carrier/Am Stan when installed incorrectly will be your lemon and be nothing but problems and a disposable unit that you will replace well within the 10-12years as per consumer reports (Even as low as 6-7 years) of service if installed incorrectly.
We still service units that are over 40 years old, not becuase we like seeing the low energy efficiency, but because they were installed correctly, serviced competently and the homeowner just decided "I am going to wait till it dies." When the homeonwner is elderly, they really do consider "Savings to Investment" ratio.
Since HVAC systems are not negative pressure systems but rather rely on the higher pressure in a room to "push" returning air back to the blower, there is absolutely no reason to not use wall cavities for return air and/or for transfer passages. It is done all the time in the best of houses.
Must be a difference in construction methods or quality in Florida. There are no problems such as this in other parts of the country. No difference between a joist space and a duct that hasn't been sealed at every joint.
Return chases should only be in interior walls, so where would any leakage wind up coming from; another interior space. Just makes no difference.
Carrier 24ANA1 Unit installed - some answers and some Questions !
OK - The return vents that I am looking at are 14 x 14's and will be in the ceiling (somewhat access limited with the re-exisiting structure). The supply side vents are on the wall near the top in each room. I am assuming that the returns even in the ceiling would help with the air flow. Ideally I would like them opposite the supplies but for a situation where the AC is the primary use item (Austin Texas gets HOT) I think that pulling the hot air back in from the top would be OK. In the winter this will not be ideal but thankfully winters are short !
The unit was installed without the returns (scheduling snafu). I am still contemplating having them put in the returns in the bedrooms to improve airflow with the doors closed. I went with the 24ANA1 scroll compressor. I am not sure what Carrier coil I got on this puppy but I did get the extended 10 year parts / labor just in case. If there is a way to determine the coil type from carrier let me know. I was surprised how small the furnace and coil were on this unit. Thankfully they were not as large as the condensor !
The Carrier 24ANA1 unit is great. I am very happy with the variable speed fan in the bedrooms. The low speed fan and de-humidify / low AC mode is very quite and is almost un-detectable. Outside the condensor is HUGE ! If you are thinking of this unit make sure you have lots of space outside for this. The outside unit is not noisy but not silent. Not sure if the scroll is really any quieter than the recip ? Certainly quieter than the old TRANE XLE 1100 it sits next to (Downstairs unit is still going strong). The scroll SEER and EER where a bit higher on the scroll and I figured to go with the unit that represented the best efficiency and newest tech.