Good questions.

I assume I set the top of my zone 2 at 142 bpm?

Your drift was almost zero, so you can probably go with 145, maybe even 150. For now, because the test was shorter than designed, I would go with 145 until you can confirm it with another test. Next time, start between 145 and 150.

Does heat play into this as they like to keep the gym at work hot, I was soaked from head to toe.

Yes, absolutely. Heart rate doesn’t measure just workout intensity, but total stress. So heat, dehydration, work, relationships, finances, etc all play a factor. It’s probably best to find a different gym to do these tests. (I’m amazed why anyone would keep a gym warm unless it’s not really used that much.)

Also if I chatted with someone too long, my HR spiked up to 150…

That’s normal.

…back to nose breathing…

Sorry for the confusion. Use nasal breathing or the drift test, not both. We’ve moved away from nasal breathing because we discovered that those with an under-developed aerobic system can nose breathe above AeT. It does work well for highly-conditioned athletes though.

Not sure if being on blood thinners would affect this test or not.

I’m not sure either. That would be a question for a doctor. I doubt a typical doctor will know what a drift test is, or what aerobic threshold is, but they should be able to let you know how it may affect heart rate during exercise.

Treadmill was set to 10% and speed of 3.6.

Once you nail down the speed that elicits a heart rate drift of 5% or less, you can train by that speed and incline whenever using the same treadmill. (And other treadmills if you’re confident that they’re accurate, which many are not.) When training by pace, you can ignore heart rate for those sessions. (We use heart rate as an imperfect substitute for pace or power.)