My wife and I thought we were going to have a major problem renting out one of her homes because of cat urine. A young male cat that had not been neutered had been kept in a 15’ X 20’ room with panelled walls. He originally used the litter box, but for the last 6 to 7 months he sprayed those panelled walls all around the complete perimeter of that living room about 12"-15" above the floor. The smell of cat urine was very strong.
A friend of ours at church sells a line of ozone and air purifiers. He gave us one to take home to use as a demonstration of the capabilities of his machines. We turned the machine on high, turned the a/c on “fan only” and left it on all weekend.
The urine smell is gone and the place is rented!! We did not have to use kilz or paint the wood paneling. The urine stains are gone also!! (Our friend suggested wetting the walls with a 50-50 mixture of white vinegar and water before starting the process, which we did. I don’t know the science behind it, but it worked)
I recommend using the ozone machine. In fact, I am going to take one of them to use on a Land/Home property. New carpets have been installed, but there is still a pet smell that needs zapping with the ozone machine before we sell it.
If you want my friends contact info, let me know.