How to clean cat urine odors out of an old house?

Try Nature's Miracle, it is an enzyme cleaner available at pet stores.

They sell enzyme eaters made for cat pee. You have to dampen the area with it. Check pet stores. Once the urine soaks into the wood you will never be 100% free of it. When the humidity kicks in during summer months you may smell it a bit unless you have a humidifier/dehumidifier on your furnace. Once you have cleaned the wood the best you can and it has THOROUGHLY dried put several layers newspaper on top of the area for several weeks topping with a throw rug to weight down., replacing it every a few days. This will remove more of the odor. It does go away in time unless the wood is dampened again, mostly by humidity in the air. So use a dehumidifier in the summer in that area if you don't have one on your furnace should you smell any remnants again.

Lived with cats all of my life so I know what you are dealing with.

Try some of these tips: https://www.craftylittlegnome.com/whole-house-smells-like-dog-urine/

Unfortunately, you can't. We had a similar problem, and when we talked to cleaning professionals, they told us that if the wood is soaked with cat urine, the smell will never come out 100%. We were told we had two options:

1) reseal the wood (but this is not a permanent solution. Eventually the smell will seep through again).

2) replace the wood. We ended up doing that option. The cleaners we talked to didn't recommend someone, so they weren't trying to shill for someone. We ended up replacing the wood flooring ourselves. It wasn't as hard a we thought it would be. We also had to replace the subflooring, as the urine had soaked through there too.

Someone else told us about another solution used by professionals which is to ozone bomb the house. You seal the house up and run an ozone machine in it for 24 hours. This will neutralize every smell in the house including cat urine. Ozone is bad for various things so it is best if the house is empty when this is done. A caveat about this process: ozone can bleach things (pictures, fabrics, paints, wallpaper) and even make some plastics age faster but still an option for some cases.

Try an enzyme eater from the pet stores. There are several brands. Make sure you do the walls as it is probably not just the floors if the cat(s) sprayed.

Thanks.