Splitting utilities in a duplex

[David Nelsen]

We are about to close on a duplex that has separate electric but only one furnace, AC and hot water heater. Anyone have ideas on how to best split the utilities or bill back to the renters?

Currently there is only one thermostat at the lower unit so I can see them cranking up the heat and then the renter upstairs is roasting so they open all the windows (duplex is in Wisconsin, so cold winters)

We looked into electronic dampers with a second thermostat upstairs, but still have concerns about how to best / fairly split the bill. (The AC is on the downstairs unit electric bill).

Thanks!