Having been part of evangelical Calvinist fellowships all my life, I've never seen them "damning everyone who's not in their group..." The doctrine of predestination says that the Father knows who the elect are, and no one else... His calling is specifically effective, and not an anemic "call to everyone equally" like non-Calvinists like to claim. If God calls everyone, then He must be a most unpersuasive Guy, as it appears a majority of people reject God from birth onwards.
I, like every other responsible Calvinist I know, believe there are myriads of non-Calvinist believers on earth...as faith alone saves...
Of course we think there are no non-Calvinists in heaven...only ones who formerly didn't understand while on earth...
Now there's an oxymoron. "Evangelical" means 'carrying the good news to those in need.' as in "evangelism". Where's the "good news" in "so sorry, I'm telling you this story, but you're not included. [It's only us.] Have a happy eternity in Hell."
Of course we think there are no non-Calvinists in heaven.
I think this statement even tops the one (by one of your co-religionists on a FR thread a month or two ago) that "Christ was a Calvinist."
I suppose it would be too much to ask you to find that verse in the Bible. [You know, "Thus saith the Lord, 'There are no non-Calvinists in Heaven.'") Nah, forget it. A closed mind is a terrible thing to waste.