The actual unit maintenance is virtually the same as a regular HVAC, mostly be sure filtration is clean. 

Forced air heat. 

I've dealt with bad tenants and having these tenants is a breath of fresh air.

People have to remember to clean them and put water in them.I’d be concerned that warm moist air is being blown inside the unit.

We're trying to decide on what material to use to replace it.There's not great air flow to inside which is why we're considering moving away from carpet and something that may hold less moisture, easier to clean, look more modern etc.

It looks like the listing mentioned forced air.

I prefer having the air space under the metal, the strapping helps to level out the uneven surface and the metal is more securely held down with strapping.

Now, how an "appraisal" works on a commercial property like this is beyond me, or if they're just having an agent pull a number out of the air and call it an appraisal. 

Looking back, may have just kept the wall units but central air seems to be a big draw for the renters.Future: Am looking into getting a HELOC on property to fund the next multifamily investment.

@Giridhara Gowdra chandrannaA - fine expensive well cared for yards and homes owned by professionals and business owners.Luxury cars B- average blue collar suburbia most homes are owner occupied and yards are in good condition.C mostly low Income people rundown rental houses lots of old apartment houses lots of old cars D VIrtually all buIldIngs are old and need some maIntenance .mostly rentals 15-25 year old cars random crIme drugs -hIgh grass and hIgh resIdents Seen walkIng around aImlesslessly F boarded up houses shootIngs no one works open aIr drug deals most everyone looks shady .Hookers rap musIc blasted from random homes and cars