I'll respond to all questions in order:
How many litter boxes do you have?
We have one litter box, on the same floor that he is peeing, it's actually closer than where he pees.
What about the kind of litter you're using?
It's a brand from Costco, it's called QualiCat. It's clumping, he still uses the litter box but seemingly less and less.
What are you using to clean up the mess?
We've tried everything, vinegar, soap, BustIt by catit, Baking Soda. We even tried cat repellent.
Where is the spot that he keeps peeing? Can you either make it less attractive for him to pee there (like by putting tinfoil or some of that vinyl carpet protector stuff with the nubby side up), or maybe place a litter box there and very gradually move it to where you want it?
The spot is on the carpet further away from his litter box, so he's actually passing his litter box to go pee there. It's around our workout equipment (treadmill, bike and elliptical trainer if it matters). He loves to play with tinfoil, and there isn't really much space there for anything else. Also, if we turn him away from one spot, he'll pick another, it's already happened once. XD
When was his last urinalysis? Do you have a copy of the results?
I'm not sure, my mom takes care of the vet stuff.
Have you tried Dr. Elsey's Cat Attract litter?
I have never heard of it, so no.
And lastly, what does he eat?
He eats Nutrience Hairball and he eats like a pig.
What kind of heart meds? One of our dogs is on a water pill for heart problems--one of the side effects is increased drinking and increased urination... Not a perfect solution, but would it be possible to adjust the meds to a lower dose?
I'm not sure exactly what they are called but they definitely make him drink more. Unfortunately they are at the lowest dose they can go. Henry's heart murmur is extremely bad so he needs lots of meds just to stabilize his heart.
Is the litter box too high for him to get onto? In a spot that is noisy?
The box is directly on the floor. It's always been in the same spot, so I don't think that's the problem. He didn't do this before.
And for everyone else, here we are: