Who changes your furnace air filter?

[John M.]

I'm new to renting, and this is one of the many small details I don't have the answer to.
It would be free for me to ask my renters to change the air filter in the furnace every month, but I'm skeptical they would do it.

What does everyone else do?
Is there a good trick, like maybe signing a HVAC contract with a major service provider, or something like that?

Thanks

[Dawn Anastasi]

You let them know how changing the filter saves them money. My tenants pay their own heat/electric. So they have an incentive to keep them clean.