Further your statement that CO is heavier than air is totally incorrect. CO is so close to the molecular weight of air that it mixes easily making it very dangerous.
Okay, so you're saying that I claimed CO is heavier than air: Where did I claim this? It's basic science and something *every* licensed technician is painfully aware of.
But moving past you putting words in my mouth, let's stop and unpack something for a moment. You claim that your local fire codes say that LP appliances can't be in a basement because propane is heavier than air.
Then you tell us that you are using LP in a basement. Using portable cylinders that are definitely not rated or approved for indoor use.
I'm not aware of any jurisdictions that ban the install of LP burning appliances in basements whole cloth; but you're seriously telling us that not only is it against your local fire code to do what you're doing, but that you're doing so using LP cylinders which are *never* ok to use in an occupied residential structure. That's not even touching on the fact that most jurisdictions ban unqualified people from making modifications to fuel burning appliances.
Now, I can already hear you furiously pounding away at the keyboard to tell me how I'm wrong; don't waste your time, I'm not. Instead, please go ahead and call your local fire marshal or non-emergency fire department number and ask them if it's safe to operate a propane burner running on LP cylinders in your basement. Go ahead and tell them that you have a vent fan and that you modified the burner yourself. I'd put money on them telling you to immediately stop.
I'm n.ot responding further to you on this one; I've said my piece and I work too hard through the week doing this for a living to spend more of my free time educating you.
You need to stop putting yourself and others in danger.