But they are also ugly, noisy, and expensive to run, so it depends a lot on the class of property and what your goals for the property are in terms of repositioning.It isn't always as simple as just slapping in a central unit; Electrical panel and/or service upgrades are sometimes needed, and you need attic or crawl access for duct work and returns, as well as a place for the air handler to go (which often means giving up a closet). 

Running HVAC trunk lines to the old ductwork was another fun issue.I pulled the permits, had the inspections (prior to & after drywall) & passed.

Or is there an inspector or someone that can check the duct work or air leakage?

Does the home need duct work?

For some houses that are pet free they have new ductwork, never exposed to pet hair, etc. 

The decision is to either patch the current ductwork or replace it with brand new and more efficient work.

The service contract is a one year contract covering a multitude of systems and appliances needed for everyday life.Here are a few of the key things to remember:•No home inspection is required as a condition to purchase*•The contract covers certain household system components and appliances regardless of age, make, or model*•You pay a trade service fee for each occurrence, regardless of the actual cost to repair or replace the broken item(s)*Our Basic coverage includes:Heating Systems Plumbing Systems Electrical Systems Water Heater Oven/Range/Cooktop Dishwasher Built-in-Microwave Garbage Disposal Exhaust Fan Ceiling Fans Plumbing Stoppages Ductwork Or you can expand your coverage to include:Central A/C Refrigerator Clothes Washer Clothes Dryer Garage Door Opener Well Pump Pool Spa Several afforadable plans are available to fit your home and budget needs.

It was plastic and cracked all over and hideous in person.Nice A/C duct work there, though an open window.

My initial pet agreement was written by a California RE attorney (we have made modifications to it over time including explicitly stating pet deposit will be used to place unit in a pre-pet state including cleaning of duct work and furnace).  

If you do this set the thermostat yourself and put a lock box over it so the tenants can't turn it up too high or down too low.I also like the idea of closing off the duct work to the upstairs apartment and adding electric baseboard heat, this might cost you a few hundred bucks.