Thank you all for your inputs.
Last night, I insulated the stack, than I removed it, it wasn’t practical; it made the stack heavy and bulky.
I did a quick heat test with and without the uninsulated stack. I used 1.25 of charcoal briquettes on the charcoal grate. I measured the temperature right above the stone (1 to 2”), the stone was 3.5” above the cooking grates using Mighty Pizza Stone heat diffuser. The temperature reached mid 400sF in few minutes once I closed the lid, the temperature dropped by 20 Deg F once I placed the stack, I guess it created a back draft, than the temperature increased pretty quickly about 50 deg. F. The amber looking charcoal that I started with started to turn dark, even with the stack on, so I slid the lid about 1” to the back, briquettes amber color started to go back and the temperature above the stone steadily increased to low 600sF. Conclusion: a crack is better than a stack
Thank I added 3 pieces of oak wood chunks, which increased the temperature to high 800/900’s F with the lid offset by 1” to 2”. I am pretty sure I tried this with my old grills, I never got these results, I guess a thicker steel grill made a big difference. I added few more chunks once the previous one died, still, I did not have any issues with any smoke, the wood and briquettes continued to burn clean.
I am still going to keep the stack mounted on my Performer lid especially when I am burning wood, to keep exhaust fume up and away from me. I need to find a better looking and heavier gauge can to use as a base for the stack though. It will be nice if I can paint it to match the lid color or maybe silver to match Weber vent disc.
Thanks again