Because of this, the unit isn’t calling for heat as often, and a section of piping in the baseboard heating froze, so now the whole unit isn’t getting heat. 

They say their electric bill is through the roof because their heat doesn’t stay in the home.

The thing that I hope sets us apart is that we will consider sustainability is as a principle driver in the redevelopment - so air sealing, insulation improvements, new windows, doors, high performance mechanicals, solar arrays, ground or air source heat pumps, resiliency and resilient spaces (think covid inspired zoom rooms, home learning centers). 

Also keep the heat on at least 55 degrees and maybe open sink cabinet doors. 

Me being the "on call super" will always get the late night call about NO HEAT.

Leave the heat on and sinks dripping?

I'll default to a savvy local like @Remington Lyman to illuminate Ohio specifics, but in general I'd pay attention to the following on investment properties:Sewer line -- these are hidden and I want to make sure they are healthy OR I have a budget for replacement right awayHVAC - have the heating and air units been well maintained? 

I have made a great friend with the next door neighbor who always watches the property, and met another neighbor who does heating/cooling, and replaced the heating system in the house at a very fair price.

The pros with the duplex are you have 2 units with essentially one set of "cap ex" features like your roof, heating system, etc.

There is also a gas wall heater that provides 50,000 BTU, but I thought it would be nice to have a wall heater in each bedroom for supplemental heat.