Completely depends on the house.
What is the current condition on Roof, HWT, HVAC/AC, (any basement foundation issues), plumbing, sewer line to the street(this is a huge one in my market, all the clay pipes from homes built in the 50-60's need replaced) With a furnace you can get a good 20-25 years from a unit if it is properly maintained.
I have two projects going on right now. One is getting all the big stuff out of the way and is a 20K rehab. So my capX is getting destroyed up front, which i like.
Second project is in immaculate condition, needs nothing. HOWEVER, windows are original, albeit in great shape, they will need to be replaced at some point. The roof has about 10 years left. So i take those capX items into play with cash reserves.
Most of the homes in my market do not have basements and do not have A/C. Window AC units are king which is fine by me. In fact a lot don't even have dishwashers, however I always put a dishwasher in to help give me that advantage over my competition.
I digress,
You need to understand the typical lifespan of the big ticket items, and fully understand the current condition of the items in the property.