Yeah. But smarter landlords can't do squat if nobody will pay the extra rent. If there's a demand for energy efficient units, I expect the market to meet it. Landlords can try advertising the efficiency of their units but I don't know if that would succeed.

Space heat isn't an issue in Tucson. There's already a nationwide law requiring all new air conditioners to be at least SEER 13. Israel requires all units to have solar hot water heaters but it's a small country that's all desert. Arizona could pass a law like that but I don't know how well solar hot water works in Idaho or New York.

Everybody would be paying the extra rent (and less in the utility bills), so all the landlords would start out equal; it's just a question of how much it costs the landlord to deliver the X BTU/month, and thus how much of the rent they get to keep.

I expect wide regional variations in such laws; what matters is that they apply to all equivalent units in a market.