2 units without separating utilities? Ideas?

[Nicholas Diaz]

So I have a two story home with a basement I am renting. I am renting the top two floors as one unit and the basement as a separate unit. I’m planning on having the tenants pay for all utilities but trying to figure out an arrangement since utilities are not separated. I don’t want to include utilities in rent because they would have no incentive to be conservative with thermostat. I’m thinking about having main tenants (top two floors) pay all utilities and reimburse them for half every month to offset basement usage. Thoughts? Suggestions?