Duplex Furnace Dilemma

[Jordan Malara]

Hi all, I'm a new real estate investor out of Colorado Springs and I just acquired a duplex a few months back. The property was a SFH that was legally converted into a duplex some time ago and we knew when we bought the property that the 2 furnaces would need to be replaced soon since they are 40+ years old. When I had a contractor come out yesterday to give me an estimate he found out that the thermostat in the lower unit was controlling and sending heat to a few of the bedrooms in the upper unit.

After talking with the contractor more we discussed a few different options:

- Replace both furnaces and reroute the existing system so the thermostats correctly heat the units. Each furnace would cost about $3100 and the rerouting would be costly and depends upon further analysis of the overall duct layout ($8000+). 

- Replace both furnaces and leave the duct system as it is ($6200).

- Replace the two furnaces with 1 large furnace for the entire property and have only 1 thermostat ($4100).

- Replace the two furnaces with 1 large furnace for the entire property and also add A/C to the property and only have 1 thermostat ($8000). I've noticed through my tenant screening that A/C is becoming a bigger factor with higher quality tenants. I haven't had any issues filling vacancies so far, but I think it could help me fill them easier, would allow me to charge a bit extra per month, and would be better for resale in the long run. However, not a necessity.

Would love to hear if anyone has any experience with an issue like this or can offer up any advice. Thanks!