I am in the process of purchasing a 6-unit and am dealing with that same question of how to reduce heating costs, as the oil bill is by far the largest expense. I had thought about some type of sub-metering solution as well, but it seems like there is really no good way to do that.
Our other buildings are duplexes where it was relatively easy/made sense to separate the heating systems. One already had electric heat in the upstairs unit and the other duplex needed a new boiler when we purchased it anyway, so we installed a new propane boiler for heat/hot water in the large unit and a couple Rinnais in the 1-bed unit. A bit pricey up front, but we are long term buy and hold investors, so the savings on paying for tenant heat makes sense.
In the 6-unit our initial thought was to install electric heat in the units, but that can be a hard sell in Maine even though I am not convinced that electric heat is necessarily more expensive than other options (we even did a comparison last winter in our 2-unit where one is on a propane boiler w/ HWBB and the other electric, and it was about the same cost per month). There is definitely a stigma about electric heat.
So, our current thinking, rather than spend the money on electric heating units, or individual Rinnai's for each unit, is to look at energy savings and heat loss. Efficiency Maine has programs that offer rebates for multifamily upgrades: https://www.efficiencymaine.com/at-work/multifamily/ . We've had an energy audit (https://www.efficiencymaine.com/at-home/energy-audit/) done at one of our duplexes and spent about $5500 on insulation which made a huge difference in the heat loss for the whole building. We have also done window replacements and replaced analog thermostats with programmable digital thermostats.
Interested to hear if anyone else has had success with weatherization/insulating and other energy efficiency measures.
