I was in your shoes one year ago and finished this year with 3 duplexes under my belt and currently finishing my first single family.  

An old mansion 5beds 3.5 baths that had an old oil Fce with an under powered blower & lacked cold air returns in all rooms so it was not efficient at all.

Once you have a few under your belt, you can decide on how much of an inspection you want based on what you see prior to putting in an offer and what you plan on renovating.

@George Blower thanks for the info!

@Aaron Belt You mentioned the Landinvestors forum?

You may or may not have the technical aptitude, confidence, or your application might not really be feasible here.3 - Up-size your system - this might be a larger blower motor (check this first) - and if that's not an option, then you can move to up sizing your furnace/blower (if you're running a 'typical' split system).That's all I can think of. 

I wouldn't recommend a PM until you have multiple units under your belt but it all depends on your time, your comfort level, and your understanding of Landlord laws in that state.

If the blower wheel is plugged up full of hair, get an HVAC tech out to clean it.Go around the house to all of the air vents, and make sure the flaps in them are open (use the little handle/lever/knob that sticks out of the grille), and that they don't have a rug or furniture or something blocking them off.Sometimes people will turn the thermostat down and then close the vents to try to regulate the temperature - if this goes on long enough, the evaporator (A-coil, inside coil) can get ice on it, which really blocks the air flow. 

Currently i have no rentals, but i have some fix and flips under my belt.

It'll happen for the first couple, but you won't even notice once you get a few under your belt.