Landlord pays Electric up to certain amount

[Mike D.]

I'm considering buying a 12 unit that has electric heaters. I'd like to make it so that heat is included with the rent by paying for each tenants' electric bill myself. To keep people from abusing the free heat I'd like to put a clause in the lease that if the electric bill is over $100, the tenant gets billed for the overage and they must pay it in next months rent. 

Is that as simple is putting a clause in the lease? It would be some extra work billing the tenants for the overage but I've found that including all utilities is very popular around here.