I’ll have to investigate Air BnB regulations some more, but it sounds like Henderson may be promising.

Would anybody with experience on retrofitting an older duplex with central heat and air feel like offering some advice on how extensive that project can be?

In my option, if you start with something more economical and less restrictive to build, such as Tiny Houses and Air Stream campers, I think you can be on to something good.  

Replace all outlets & switchesInstall vapor barrier in crawl Space The cost of the job is as follows;-New 2 ton compressor/new coil & supplies $1100- Central air install $600- Sub panel supplies & install $500- All supplies & utilities $15,000- Labor $6,000- Appraisal $500- inspection $400- Lawyer $500- Lawyer fee for zoning correction pendingWhen we began the rehab we noticed the previous owner created a doorway between the apartments and originally the was a brick wall between the two units.

I don't think there is enough air force of pushing the heat to the rooms.

I am a newly married Air Force Family Medicine Resident Physician at Eglin AFB, Florida.

At least in that situation, you're not under the pressure of breaking even every month. 

They could be looking at it as some cash flow now but a redevelopment play to go higher with air rights and density in the future.

That is like saying a broken air conditioner in the middle of summer and a inoperable doorbell should be handle with the same level of priority.

@Waylen Herdman Louisville is a great market for air bnb as a way to house hack.