You don’t live in the units you are renting out. How do you know when things are wearing out or breaking down if your tenants don’t tell you or don’t recognize it themselves? While many tenants are responsible people, the fixtures in the house are not their stuff and there is less of a sense of ownership and stewardship over things that belong to others.
Also tenants generally don’t have to pay for the repairs when things wear out. And when they wear out catastrophically and flood or fire ensues, repairs are MUCH more expensive. Equipment failures can often happen during a time of change of use, such as when systems are not used for a while during a vacancy and then a new party comes in and everything gets turned on and turned up.
Let a home inspector keep you informed with a report on the whole house. Inspections could be done before the unit is rented out, at regular intervals or before a change in tenants. It is helpful for the inspector to ask the outgoing tenant specific questions about how everything was working because they can give valuable feedback about their experience of the day to day functioning systems of the house.
During the presentation of the inspection results, the home inspector will walk around with you and while describing the conditions, point things out so you have a better understanding of the house works, and answer your questions. This is especially helpful shortly after you buy the house, if you haven’t already had an inspection. You need to know where the water shut off is so you can tell your tenants either at time of rental or over the phone if there is a major leak. And so on for electrical, heating, A/C systems.