My situation is, I have two units (one on each floor) both with radiator heat, but the same thermostat controls both floors, and is located on the 2nd floor (top unit).I would love to give tenants in each unit the ability to control their own heat.  

That should help out to increase cash flow.Second is I would like to zone out heating system for building by floor. 

A heating unit, roof, window replacement, etc... can blow a big hole through your pro-forma.Make sure you spend the money to get a professional inspection, so you know what you're up against. 

Concrete, after curing, is very good at resisting damage from heat.  

Purchase price: $100,000 Cash invested: $115,000 Sale price: $249,900 Single Family House-1400sqft-3/1.5Actual sqft was 1600sqft and was able to convert bonus space to additional bed room and convert 1/2 bath to full.4 bedroom 2 bathroom, huge 4 car garage with hook up for in floor heating, and sits on large 1/2 acre lot.

I have a Chigo wall HVAC unit that needs servicing (heat isn't working) in my tenants property.

But I could accept the higher price because the tenants pay their own heat, hot water and electric, so I'm at 36% ROI which seems silly-good.

Nobody can predict when and how the market cycle will drop, but leveraging yourself up that much with minimal/no cash reserves and no REI experience at a time when the market is already very heated is a risky proposition and one you might want to consider building in a little safety net before jumping in. 

This tenant cane with the duplex when we purchased it and his rent is about 150 a month to cheap for one and he’s been an issue with keeping oil in the tank for the heat lol.

First the coils all need to be cleaned both inside and out.