Hi Bart, how have you been?

I am not intimately familiar with this model Superior box so I cannot help you on it. I do know there is an intentional gap on all Heatilators and most Heat&Glos for the last 15 yrs. This is where the cooling air from the bottom and side louvers dumps into the flue to:
a) cool the firebox
b) turbo charge the flue gases.

The old Heatilator Mark 123 did this using louvers at the top of the smoke chamber.

If Lennox (Superior) Tech Support cannot help, try Jimmy Kress at Specialty Supply in Cherry Hill, NJ. He sells replacement parts to sweeps for older Superior and Marco units and advertising in Alt. Energy Retailer Mag. 800-331-9234

HTH,
Bob Harper

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