-I upgraded the HVAC system / a heat pump for each floor-Upgraded the electrical / new panels / new wiring-Added an additional washer/dryer upstairs-New kitchen upstairs & down-New floors upstairs & down-New bathrooms upstairs & down-New floors upstairs & downI am planning on living in the upstairs and renting the downstairs out.  

I hid the system and put the siren in the heat duct so it would blast through the whole house.

The list as noted here has things that fall under "as is", like water taking time to heat up....that is how hot water tanks work...but doesn't allow you to avoid compliance issues. 

My brother and I have inherited and old Victorian home that’s completely payed off that I believe needs quite a bit of work (foundation, roofing and no central heat or air in place) but we have little capital.

I built that heat exchanger too that you see in the foreground. 

This is the simplest method, but it also means your tenants are more likely to abuse the utilities by leaving windows open with the heat or A/C running, leaving lights on, ignoring the toilet that constantly flushes on its own, etc.3.

It’s on knob and tube, there’s no working heat system, old single pane windows etc.

The majority of the time we are renovating buildings with landlord paid heat that have this and these ACs also, we are separating it to minisplits on the tenants electric which do heating and cooling.

The HVAC has been completely revamped to provide central AC and heat throughout the home.

They require regular maintenance and sealing plus they can be sensitive to moisture and heat.