Glad you caught this in time!
Seeing your picture of the exhaust opening, I can see why you had an issue. It would take me an hour to find a picture of my exhaust opening, but it is made so that making a nest in it would be much harder than that.
I LOVE my 38 foot Roberts-Gordon radiant heat tube heaters & have them in both the main part of the building & the paint room for 20 years now. I have NEVER had any problems with them, in fact the guy who sold them to me keeps complaining about how he can't make money off of me when they lasted so long! LOL
God Bless
Bill
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