Installing second boiler for small 2-unit

[James Albrecht]

I'm curious to get feedback on whether it would be worth the expense to install a 2nd boiler / hot water heater for a small duplex so the tenants can be responsible for their own gas usage. There is currently one mid-1980's 84% AFUE boiler with separate zones for each unit and one hot water heater. I've been told this boiler is in good condition with no issues. The water heater is older (2008), but is still functional. There are separate gas meters and electrical panels for each unit.  The upstairs tenant pays for the cooking gas for his unit, but I pay the gas bill for unit 1, which includes the gas for the boiler and hot water heater.  The recent 12 month average for natural gas comes to approx. $125 / mo.   I'm currently leaning towards keeping the equipment for unit 1 and installing a natural gas high-efficiency combi system for the small, 600 square ft upper apartment and having this system connected to that unit's gas meter and having the tenants of each unit pay for their own heat / hot water.  The cost for such a system is high.  The bids I'm getting are in the $13,000 - $15,000 range.  However, I can finance this and depending on the financing option I go with can likely get the monthly cost down to about what I'm already paying for the average monthly natural gas bill.  Then my cost is fixed and not subject to rising natural gas prices or varying usage and weather conditions in the future and obviously once the system is paid off will significantly improve cashflow on this property. It would also add value to the property. The main downside I can think of is having two systems to maintain instead of one, although the new system will likely be under warranty for a while.  I've also considered billing the tenants for their portion of gas usage based on square footage using RUBS, but this sounds like a hassle. Just curious what other investor's thoughts are on the best move.  Thanks